Predicting polarization enhancement in multicomponent ferroelectric superlattices

Ab initio calculations are utilized as an input to develop a simple model of polarization in epitaxial short-period CaTiO3/SrTiO3/BaTiO3 superlattices grown on a SrTiO3 substrate. The model is then combined with a genetic algorithm technique to optimize the arrangement of individual CaTiO3, SrTiO3 and BaTiO3 layers in a superlattice, predicting structures with the highest possible polarization and a low in-plane lattice constant mismatch with the substrate. This modelling procedure can be applied to a wide range of layered perovskite-oxide nanostructures providing guidance for experimental development of nanoelectromechanical devices with substantially improved polar properties.Comment: 4 pages, submitted to PR

Integer Programming and Incidence Treedepth

Recently a strong connection has been shown between the tractability of integer programming (IP) with bounded coefficients on the one side and the structure of its constraint matrix on the other side. To that end, integer linear programming is fixed-parameter tractable with respect to the primal (or dual) treedepth of the Gaifman graph of its constraint matrix and the largest coefficient (in absolute value). Motivated by this, Koutecký, Levin, and Onn [ICALP 2018] asked whether it is possible to extend these result to a more broader class of integer linear programs. More formally, is integer linear programming fixed-parameter tractable with respect to the incidence treedepth of its constraint matrix and the largest coefficient (in absolute value)? We answer this question in negative. We prove that deciding the feasibility of a system in the standard form, Ax=b,l≤x≤u , is NP-hard even when the absolute value of any coefficient in A is 1 and the incidence treedepth of A is 5. Consequently, it is not possible to decide feasibility in polynomial time even if both the assumed parameters are constant, unless P=NP

Hypersensitivity and chaos signatures in the quantum baker's maps

Classical chaotic systems are distinguished by their sensitive dependence on initial conditions. The absence of this property in quantum systems has lead to a number of proposals for perturbation-based characterizations of quantum chaos, including linear growth of entropy, exponential decay of fidelity, and hypersensitivity to perturbation. All of these accurately predict chaos in the classical limit, but it is not clear that they behave the same far from the classical realm. We investigate the dynamics of a family of quantizations of the baker's map, which range from a highly entangling unitary transformation to an essentially trivial shift map. Linear entropy growth and fidelity decay are exhibited by this entire family of maps, but hypersensitivity distinguishes between the simple dynamics of the trivial shift map and the more complicated dynamics of the other quantizations. This conclusion is supported by an analytical argument for short times and numerical evidence at later times.Comment: 32 pages, 6 figure

Use of the q-Gaussian mutation in evolutionary algorithms

Copyright @ Springer-Verlag 2010.This paper proposes the use of the q-Gaussian mutation with self-adaptation of the shape of the mutation distribution in evolutionary algorithms. The shape of the q-Gaussian mutation distribution is controlled by a real parameter q. In the proposed method, the real parameter q of the q-Gaussian mutation is encoded in the chromosome of individuals and hence is allowed to evolve during the evolutionary process. In order to test the new mutation operator, evolution strategy and evolutionary programming algorithms with self-adapted q-Gaussian mutation generated from anisotropic and isotropic distributions are presented. The theoretical analysis of the q-Gaussian mutation is also provided. In the experimental study, the q-Gaussian mutation is compared to Gaussian and Cauchy mutations in the optimization of a set of test functions. Experimental results show the efficiency of the proposed method of self-adapting the mutation distribution in evolutionary algorithms.This work was supported in part by FAPESP and CNPq in Brazil and in part by the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant EP/E060722/1 and Grant EP/E060722/2

Does Providing Assistance to Children and Adolescents Increase Repeatability and Plausibility of Self-Reporting Using a Web-Based Dietary Recall Instrument?

Background: It is important to find ways to minimize errors when children self-report food consumption. Objective: The objective of this study was to investigate whether assistance given to children completing a self-administered 24-hour dietary recall instrument called SACANA (Self-Administered Child, Adolescent and Adult Nutrition Assessment) increased the repeatability and plausibility of energy intake (EI) estimates. Participants/setting: The study was conducted between October 2013 and March 2016 in a convenience sample of 395 children, aged 8 to 17 years, from eight European countries participating in the I.Family study. Design: SACANA was used to recall the previous day's food intake, twice in a day, once with and once without assistance. Main outcome measures: The difference in EI between the first and second recalls was the main repeatability measure; the ratio of EI to basal metabolic rate was the plausibility measure. Statistical methods: Generalized linear mixed models, adjusted for sex, age, and body mass index z-score, were used to assess whether assistance during the first vs second recall influenced repeatability and plausibility. Results: The difference in estimated EI (EI from second recall minus EI from first recall) was significantly lower (P<0.001) in those assisted at first (median=-76 kcal) than those assisted at second recall (median=282 kcal). Modeling showed that EI at assisted first recall was 19% higher (95% CI 1.13 to 1.24) than in assisted second recall. Overall, 60% of recalls had a plausible EI. Modeling to estimate the simultaneous effects of second vs first recall and assistance vs no assistance on plausibility showed that those assisted at first recall had significantly higher odds of a plausible recall than those unassisted (odds ratio 3.64, 95% CI 2.20 to 6.01), with no significant difference in plausibility of second recall compared to the first (odds ratio 1.48, 95% CI 0.92 to 2.35). Conclusions: When children are assisted at first recall, the plausibility and repeatability of the later unassisted recall improve. This improvement was evident for all ages. A future, adequately powered study is required to investigate the age range for which assistance is advisable

Technical Note: Four‐dimensional deformable digital phantom for MRI sequence development

From Wiley via Jisc Publications RouterHistory: received 2021-02-04, rev-recd 2021-05-14, accepted 2021-05-26, pub-electronic 2021-08-02Article version: VoRPublication status: PublishedFunder: Engineering and Physical Sciences Research Council; Id: http://dx.doi.org/10.13039/501100000266; Grant(s): EP/R5131631/1Funder: NIHR Manchester Biomedical Research CentreFunder: Cancer Research UK; Id: http://dx.doi.org/10.13039/501100000289; Grant(s): A21993Abstract: Purpose: MR‐guided radiotherapy has different requirements for the images than diagnostic radiology, thus requiring development of novel imaging sequences. MRI simulation is an excellent tool for optimizing these new sequences; however, currently available software does not provide all the necessary features. In this paper, we present a digital framework for testing MRI sequences that incorporates anatomical structure, respiratory motion, and realistic presentation of MR physics. Methods: The extended Cardiac‐Torso (XCAT) software was used to create T1, T2, and proton density maps that formed the anatomical structure of the phantom. Respiratory motion model was based on the XCAT deformation vector fields, modified to create a motion model driven by a respiration signal. MRI simulation was carried out with JEMRIS, an open source Bloch simulator. We developed an extension for JEMRIS, which calculates the motion of each spin independently, allowing for deformable motion. Results: The performance of the framework was demonstrated through simulating the acquisition of a two‐dimensional (2D) cine and demonstrating expected motion ghosts from T2 weighted spin echo acquisitions with different respiratory patterns. All simulations were consistent with behavior previously described in literature. Simulations with deformable motion were not more time consuming than with rigid motion. Conclusions: We present a deformable four‐dimensional (4D) digital phantom framework for MR sequence development. The framework incorporates anatomical structure, realistic breathing patterns, deformable motion, and Bloch simulation to achieve accurate simulation of MRI. This method is particularly relevant for testing novel imaging sequences for the purpose of MR‐guided radiotherapy in lungs and abdomen

Food and beverage intakes according to physical activity levels in European children: The IDEFICS (Identification and prevention of Dietary and lifestyle induced health EFfects in Children and infantS) study

Objective Physical activity (PA) levels and dietary habits are considered some of the most important factors associated with obesity. The present study aimed to examine the association between PA level and food and beverage consumption in European children (2-10 years old).Design/Setting/Subjects A sample of 7229 children (49·0 % girls) from eight European countries participating in the IDEFICS (Identification and prevention of Dietary and lifestyle induced health EFfects In Children and infantS) study was included. Moderate-to-vigorous PA (MVPA) was assessed objectively with accelerometers. FFQ was used to register dietary habits. ANCOVA and binary logistic regression were applied.Results Boys who spent less time in MVPA reported lower consumption of vegetables, fruits, cereals, yoghurt, milk, bread, pasta, candies and sugar-sweetened beverages (SSB) than boys who spent more time in MVPA (P<0·05). Moreover, boys who spent less time in MVPA were more likely to consume fast foods and water than those in the highest MVPA tertile (P<0·05). Girls who spent less time in MVPA reported lower consumption frequencies of vegetables, pasta, bread, yoghurt, candies, jam/honey and SSB than girls in the highest MVPA tertile (P<0·05). Also, girls in the lowest MVPA tertile were more likely to consume fast foods and water than those with high levels of MVPA (P<0·05).Conclusions Food intake among European children varied with different levels of daily MVPA. Low time spent in MVPA was associated with lowest consumption of both high- and low-energy-dense foods and high fast-food consumption

From evolutionary computation to the evolution of things

Evolution has provided a source of inspiration for algorithm designers since the birth of computers. The resulting field, evolutionary computation, has been successful in solving engineering tasks ranging in outlook from the molecular to the astronomical. Today, the field is entering a new phase as evolutionary algorithms that take place in hardware are developed, opening up new avenues towards autonomous machines that can adapt to their environment. We discuss how evolutionary computation compares with natural evolution and what its benefits are relative to other computing approaches, and we introduce the emerging area of artificial evolution in physical systems

Monotonicity of Fitness Landscapes and Mutation Rate Control

A common view in evolutionary biology is that mutation rates are minimised. However, studies in combinatorial optimisation and search have shown a clear advantage of using variable mutation rates as a control parameter to optimise the performance of evolutionary algorithms. Much biological theory in this area is based on Ronald Fisher's work, who used Euclidean geometry to study the relation between mutation size and expected fitness of the offspring in infinite phenotypic spaces. Here we reconsider this theory based on the alternative geometry of discrete and finite spaces of DNA sequences. First, we consider the geometric case of fitness being isomorphic to distance from an optimum, and show how problems of optimal mutation rate control can be solved exactly or approximately depending on additional constraints of the problem. Then we consider the general case of fitness communicating only partial information about the distance. We define weak monotonicity of fitness landscapes and prove that this property holds in all landscapes that are continuous and open at the optimum. This theoretical result motivates our hypothesis that optimal mutation rate functions in such landscapes will increase when fitness decreases in some neighbourhood of an optimum, resembling the control functions derived in the geometric case. We test this hypothesis experimentally by analysing approximately optimal mutation rate control functions in 115 complete landscapes of binding scores between DNA sequences and transcription factors. Our findings support the hypothesis and find that the increase of mutation rate is more rapid in landscapes that are less monotonic (more rugged). We discuss the relevance of these findings to living organisms