Transport and fluctuation-dissipation relations in asymptotic and pre-asymptotic diffusion across channels with variable section

We study the asymptotic and pre-asymptotic diffusive properties of Brownian particles in channels whose section varies periodically in space. The effective diffusion coefficient $D_{\mathrm{eff}}$ is numerically determined by the asymptotic behavior of the root mean square displacement in different geometries, considering even cases of steep variations of the channel boundaries. Moreover, we compared the numerical results to the predictions from the various corrections proposed in the literature to the well known Fick-Jacobs approximation. Building an effective one dimensional equation for the longitudinal diffusion, we obtain an approximation for the effective diffusion coefficient. Such a result goes beyond a perturbation approach, and it is in good agreement with the actual values obtained by the numerical simulations. We discuss also the pre-asymptotic diffusion which is observed up to a crossover time whose value, in the presence of strong spatial variation of the channel cross section, can be very large. In addition, we show how the Einstein's relation between the mean drift induced by a small external field and the mean square displacement of the unperturbed system is valid in both asymptotic and pre-asymptotic regimes.Comment: RevTeX 4-1, 11 Pages, 11 pdf figure

The executive functions in overweight and obesity: a systematic review of neuropsychological cross-sectional and longitudinal studies

Background: The increasing incidence of people affected by overweight or obesity is a significant health problem. The knowledge of the factors which influences the inappropriate eating behaviors causing excessive body fat is an essential goal for the research. Overweight and obesity are significant risk factors for many health diseases, such as cardiovascular problems, diabetes. Recently, many studies have focused on the relationship between body weight and cognitive processes. Objectives: This systematic review is aimed to investigate the existence and the nature of the relationship between excessive body weight (overweight/obesity) and executive functions, analyzing cross-sectional, and longitudinal studies in order to verify the evidence of a possible causality between these variables. Methods: The review was carried out according to the PRISMA-Statement, through systematic searches in the scientific databases PubMed, Medline, PsychInfo, and PsycArticles. The studies selected examined performance on executive tasks by participants with overweight or obesity, aged between 5 and 70 years. Studies examining eating disorders or obesity resulting from other medical problems were excluded. Furthermore, the results of studies using a cross-sectional design and those using a longitudinal one were separately investigated. Results: Sixty-three cross-sectional studies and twenty-eight longitudinal studies that met our inclusion and exclusion criteria were analyzed. The results confirmed the presence of a relation between executive functions and overweight/obesity, although the directionality of this relation was not clear; nor did any single executive function emerge as being more involved than others in this relation. Despite this, there was evidence of a reciprocal influence between executive functions and overweight/obesity. Conclusions: This systematic review underlines the presence of a relationship between executive functions and overweight/obesity. Moreover, it seems to suggest a bidirectional trend in this relationship that could be the cause of the failure of interventions for weight reduction. The results of this review highlight the importance of a theoretical model able to consider all the main variables of interest, with the aim to structuring integrated approaches to solve the overweight/obesity problems

Anomalous diffusion and response in branched systems: a simple analysis

We revisit the diffusion properties and the mean drift induced by an external field of a random walk process in a class of branched structures, as the comb lattice and the linear chains of plaquettes. A simple treatment based on scaling arguments is able to predict the correct anomalous regime for different topologies. In addition, we show that even in the presence of anomalous diffusion, Einstein's relation still holds, implying a proportionality between the mean square displacement of the unperturbed systems and the drift induced by an external forcing.Comment: revtex.4-1, 16 pages, 7 figure

Executive functions in the elderly with Mild Cognitive Impairment: a systematic review on motor and cognitive inhibition, conflict control and cognitive flexibility

Background: Mild Cognitive Impairment (MCI) is a syndrome characterised by mild cognitive decline, on one or more domains, but which does not compromise daily functions. Several studies have investigated the relationship between MCI and deficit in executive functions (EFs) but, unlike robust evidence in the mnestic domain, the nature of executive deficits in the MCI population remains uncertain. Objectives: This systematic review aims to evaluate EFs in patients with MCI, considering inhibition (motor and cognitive), conflict control and cognitive flexibility. Method: The databases used for the search were PUBMED, PsycINFO, PsycARTICLES and MEDLINE. Eligibility criteria: use of specific paradigms for EFs assessment ("Wisconsin Card Sorting Test", "Stroop Task", "Go/No-Go Task", "Flanker Task"); age over 65, studies published in English. Exclusion criteria: presence of dementia; psychiatric disorders; stroke; cranial trauma; inclusion of participants with MCI in groups with healthy elderly or those with dementia. Results: Fifty-five studies were selected, namely: Stroop Task (N=30), WCST (N=14), Go/No-Go (N=9), Flanker Task (N=2). Results have shown in people with MCI deficits in all the EFs considered. Conclusions: The results of this review support the applicability of the four experimental tasks examined for the study of EFs in people with MCI. These paradigms are useful in research, diagnosis and therapeutic purposes, allowing obtaining an articulated EFs profile that can compromise the daily life in elderly. These EFs are not generally evaluated by standard assessment of MCI, but their evaluation can lead to a better knowledge of MCI and help in the diagnosis and treatment

Synthesis of Disentangled Ultra-High Molecular Weight Polyethylene: Influence of Reaction Medium on Material Properties

The polymerization of ethylene to Ultra-High Molecular Weight Polyethylene (UHMWPE) in certain reaction conditions allows synthesis of nascent powders with a considerably lower amount of entanglements: the material obtained is of great interest from both academic and industrial viewpoints. From an academic point of view, it is interesting to follow the evolution of the metastable melt state with the progressive entanglements formation. Industrially, it is valuable to have a solvent-free processing route for the production of high modulus, high strength tapes. Since the polymer synthesis is performed in the presence of a solvent, it is interesting to investigate the influence that the reaction medium can have on the catalyst activity, resultant molecular characteristics, and polymer morphology at the macroscopic as wells as microscopic level. In this paper, we present the effect that two typical polymerization solvents, toluene and heptane, and mixtures of them, have on the catalytic performance and on the polymer properties. The observations are that an unexpected increase of catalyst activity, accompanied by a significant improvement in mechanical properties, is found when using a carefully chosen mixture of solvents. A tentative explanation is given on the basis of the presented results

The Impact of Migration on Productivity:Evidence from the United Kingdom

The UK saw a sharp rise in work-related migration, particularly from the EU, in the 2000s and 2010s, with profound impacts on the labour market. We investigate the relationship between migration and productivity in Great Britain between 2002 and 2018, using an instrumental variable approach which follows the commonly used shift-share methodology. Our results, which are robust to a variety of tests, suggest that immigration has a positive and significant impact (in both the statistical sense and more broadly) on productivity, as measured by GVA per job at the Travel-to-Work-Area level. We indeed find that a 1 p.p. increase in the share of migrants is associated with a 0.84 % increase in productivity in 2SLS estimates. We discuss the implications for post-Brexit immigration policy.</p

Synthesis of disentangled Ultra-High Molecular Weight Polyethylene: influence of reaction medium on material properties

The polymerization of ethylene to Ultra-High Molecular Weight Polyethylene (UHMWPE) in certain reaction conditions allows synthesis of nascent powders with a considerably lower amount of entanglements: the material obtained is of great interest from both academic and industrial viewpoints. From an academic point of view, it is interesting to follow the evolution of the metastable melt state with the progressive entanglements formation. Industrially, it is valuable to have a solvent-free processing route for the production of high modulus, high strength tapes. Since the polymer synthesis is performed in the presence of a solvent, it is interesting to investigate the influence that the reaction medium can have on the catalyst activity, resultant molecular characteristics and polymer morphology at the macroscopic as wells as microscopic level. In this paper we present the effect that two typical polymerization solvents, toluene and heptane, and mixtures of them, have on the catalytic performance and on the polymer properties. The observations are that an unexpected increase of catalyst activity, accompanied by a significant improvement in mechanical properties, is found when using a carefully chosen mixture of solvents. A tentative explanation is given on the basis of the presented results

First results of a GNSS-R experiment from a stratospheric balloon over boreal forests

The empirical results of a global navigation satellite systems reflectometry (GNSS-R) experiment onboard the Balloon EXperiments for University Students (BEXUS) 17 stratospheric balloon performed north of Sweden over boreal forests show that the power of the reflected signals is nearly independent of the platform height for a high coherent integration time T-c = 20 ms. This experimental evidence shows a strong coherent component in the forward scattered signal, as compared with the incoherent component, that allows to be tracked. The bistatic coherent reflectivity is also evaluated as a function of the elevation angle, showing a decrease of similar to 6 dB when the elevation angle increases from 35. to 70 degrees. The received power presents a clearly multimodal behavior, which also suggests that the coherent scattering component may be taking place in different forest elements, i.e., soil, canopy, and through multiple reflections canopy-soil and soil-trunk. This experiment has provided the first GNSS-R data set over boreal forests. The evaluation of these results can be useful for the feasibility study of this technique to perform biomass monitoring that is a key factor to analyze the carbon cycle.Peer ReviewedPostprint (author's final draft

Use of PLIF to investigate mixing of immiscible liquids in static mixer

The performance of Kenics (KM) and Sulzer (SMX+) designs of static mixer has been investigated for the mixing of immiscible fluids using in situ optical measurements. The fluids used are water as the continuous phase and either silicone oil in the presence of surfactant (Sodium Lauryl Ether Sulfate), or Lytol mineral oil in the presence of a nonionic surfactant (Span 80). The dispersed phase volume fraction was between 0.0072% and 0.028 % and the superficial velocities ranged from 0.16 to 0.91 m/s. The pipe diameter was 0.0127 m and 6 or 12 mixing elements were used for each mixer type. Planar Laser Induced Fluorescence (PLIF) has been used to obtain images of the droplets formed in a traverse section across the mixer outlet. Image analysis methods have been developed, based upon the areal distribution and individual striation methods proposed by Alberini et al. (2014a, 2014b) for the blending of miscible fluids. The analysis enables drop size distributions to be obtained as a function of the number of mixing elements, interfacial tension and superficial velocity. A model for the drop size distribution has been developed in order to predict mixer performance a priori

Diffusive processes in systems with geometrical constraints: from lattice models to continuous channels

We focus on the Brownian motion within channels with varying cross – section as well as on the diffusion on branched structures, a subject particularly relevant for the modeling of the passive transport process within living cells, which are characterized by a naturally constrained environment and the motion, at least on the length scales of the macromolecules, is well described by diffusion rather than bulk flow. In particular, we studied the occurrence of anomalous transport in a variety of branched structures and fractal trees. We proved that the Fluctuation Dissipation Relation (FDR) can be extended, in some cases, to the anomalous transport regime, at least within the linear response approximation. On the other hand, We pointed out how the FDR can be broken by choosing properly the branching of the analyzed structure, as a consequence of the emergence of an “entropic” drift due to the high ramifications introduced. This result suggests that FDRs are more sensitive to the geometrical structure rather than to the details of the dynamics. We also analyzed, in contrast to those examples showing anomalous diffusion, a series of situations characterized by a standard scaling of the MSD (and/or of the higher order moments), however with a non Gaussian probability density, thus showing how standard diffusion is not always Gaussian