Linear Boltzmann dynamics in a strip with large reflective obstacles: stationary state and residence time

The presence of obstacles modify the way in which particles diffuse. In cells, for instance, it is observed that, due to the presence of macromolecules playing the role of obstacles, the mean square displacement ofbiomolecules scales as a power law with exponent smaller than one. On the other hand, different situations in grain and pedestrian dynamics in which the presence of an obstacle accelerate the dynamics are known. We focus on the time, called residence time, needed by particles to cross a strip assuming that the dynamics inside the strip follows the linear Boltzmann dynamics. We find that the residence time is not monotonic with the sizeand the location of the obstacles, since the obstacle can force those particles that eventually cross the strip to spend a smaller time in the strip itself. We focus on the case of a rectangular strip with two open sides and two reflective sides and we consider reflective obstaclea into the strip

Residence time of symmetric random walkers in a strip with large reflective obstacles

We study the effect of a large obstacle on the so called residence time, i.e., the time that a particle performing a symmetric random walk in a rectangular (2D) domain needs to cross the strip. We observe a complex behavior, that is we find out that the residence time does not depend monotonically on the geometric properties of the obstacle, such as its width, length, and position. In some cases, due to the presence of the obstacle, the mean residence time is shorter with respect to the one measured for the obstacle--free strip. We explain the residence time behavior by developing a 1D analog of the 2D model where the role of the obstacle is played by two defect sites having a smaller probability to be crossed with respect to all the other regular sites. The 1D and 2D models behave similarly, but in the 1D case we are able to compute exactly the residence time finding a perfect match with the Monte Carlo simulations

Making Emotion Visible: Felipe Trigo and \u3ci\u3eLa sed de amar (educación social)\u3c/i\u3e

In his day, Felipe Trigo (1864–1916) was a polemical yet widely appreciated author. In both his essays and fiction, he proposed and actively promoted solutions for the hysteria, melancholy, and latent violence produced by the nineteenth-century gender construct of the ángel del hogar, the initially middle-class ideal that established marriage and the home as the place for all women. Yet, in 1983, Ángel Martínez San Martín could justifiably write: “El desprecio y el olvido han sido, hasta hace muy poco, los dos más fieles compañeros de (su) obra literaria” (239). Today, most critics dismiss his work or apologize for analyzing it. For example, Roberta Johnson’s most recent book, Gender and Nation in the Spanish Modernist Novel, only states of the extremeño: “[. . .] because some of Trigo’s themes would take my discussions in diffuse directions, I do not include his works in this book” (viii). Ricardo Krauel’s discussion of suicide in Si sé por qué begins with a profuse apology for reading Trigo’s novels and a critique of his style in the mode of the most established negative criticism of Trigo’s work, in his own time and since

Heroin-piracetam mixture: suggested mechanisms of action and risks of misinterpretation for drug users

Piracetam is a positive allosteric modulator of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor that has been frequently used in the treatment of cognitive disorders. Press and internet reports indicate that the use of piracetam, as a heroin adulterant, has spread rapidly in some countries, especially in Asia and Europe. Its use, as adulterant, is believed to produce more profound desirable effects, while decreasing hangover. Recent surveys demonstrated that piracetam protects neurons from heroin-induced apoptosis. The protective role of this adulterating substance may be related to restoration of beta-endorphin levels and to its neuroprotective effects. The aim of this paper is to review the relevant literature and suggest the main hypothetical mechanisms that justify its use as a heroin adulterant, try to understand if its use could help people who want to come off heroin by reducing withdrawal symptoms and, finally, give useful information that permit us to understand why drug trafficking organisations started to use piracetam as heroin adulterant

Semi-implicit Eulerian method for the fluid structure interaction of elastic membranes

In this paper we propose a novel and general approach to design semi-implicit methods for the simulation of fluid-structure interaction problems in a fully Eulerian framework. In order to properly present the new method, we focus on the two-dimensional version of the general model developed to describe full membrane elasticity. The approach consists in treating the elastic source term by writing an evolution equation on the structure stress tensor, even if it is nonlinear. Then, it is possible to show that its semi-implicit discretization allows us to add to the linear system of the Navier-Stokes equations some consistent dissipation terms that depend on the local deformation and stiffness of the membrane. Due to the linearly implicit discretization, the approach does not need iterative solvers and can be easily applied to any Eulerian framework for fluid-structure interaction. Its stability properties are studied by performing a Von Neumann analysis on a simplified one-dimensional model and proving that, thanks to the additional dissipation, the discretized coupled system is unconditionally stable. Several numerical experiments are shown for two-dimensional problems by comparing the new method to the original explicit scheme and studying the effect of structure stiffness and mesh refinement on the membrane dynamics. The newly designed scheme is able to relax the time step restrictions that affect the explicit method and reduce crucially the computational costs, especially when very stiff membranes are under consideration

Nootropics use in the workplace. Psychiatric and ethical aftermath towards the new frontier of bioengineering

OBJECTIVE: The authors have sought to expound upon and shed a light on the rise of nootropics, which have gradually taken on a more and more relevant role in workplaces and academic settings. MATERIALS AND METHODS: Multidisciplinary databases have been delved into by entering the following keys: "nootropics", "cognitive enhancement", "workplace", "productivity", "ethics", "bioengineering". In addition, a broad-ranging search has been undertaken on institutional websites in order to identify relevant analysis and recommendations issued by international institutions and agencies. Papers and reports have been independently pored over by each author. This search strategy has led to the identification of 988 sources but only 64 were considered appropriate for the purposes of the paper after being selected by at least 3 of the authors, independently. RESULTS: The notion of an artificially enhanced work performance - carried out by the 'superworker' - is particularly noteworthy and resonates with the conception of contemporary work on so many different levels: the rising need and demands for higher degrees of flexibility and productivity on the job, the implications of a '24/7' society, where more and more services are available at any time, the ever greater emphasis on entrepreneurial spirit, individual self-reliance and self-improvement, and last but not least, the impact of an ageing society on economic standards and performance. CONCLUSIONS: Moreover, it is worth mentioning that human enhancement technologies will predictably and increasingly go hand in hand with gene editing, bioengineering, cybernetics and nanotechnology. Applications are virtually boundless, and may ultimately affect all human traits (physical strength, endurance, vision, intelligence and even personality and mood)

Numerical evidence for the approximation of dissipative systems by gyroscopically coupled oscillator chains

Inspired by the equations of motion of the gyroscope, where a Lagrangian and conservative system may appear to mimic a dissipative one when focusing on a single degree of freedom for finite time intervals, we introduce a gyroscopic-type coupling between harmonic oscillators. The aim is to propose a tentative scheme of solution for the problem of finding a higher-dimensional Lagrangian system approximating a lower-dimensional dissipative one. Specifically, we consider a certain family of Lagrangian systems, for which the time evolution of the first Lagrangian parameter is conjectured to be a good approximation for the evolution of a one-dimensional linear dissipative system in finite time intervals, up to a fixed precision. The behavior of the selected family of gyroscopic couplings is compared with a given dissipative system, properly optimizing a family of parameters according to a described scheme. Numerical calculations are reported, suggesting the validity of the proposed conjecture

A proposed role for sepsis in the pathogenesis of myocardial calcification

Myocardial calcification is a rare and life-threatening condition that is a recognised complication of ischaemic heart disease, cardiac surgery, rheumatic fever and myocarditis. It is distinct from coronary artery or valvular calcification, and can be seen in patients with abnormal calcium metabolism1 . Its presence in the context of sepsis is less well recognised and the mechanisms responsible are poorly understood. We review the relevant literature and propose a mechanistic theory for its pathogenesi

Conditional expectation of the duration of the classical gambler problem with defects

The effect of space inhomogeneities on a diffusing particle is studied in the framework of the 1D random walk. The typical time needed by a particle to cross a one--dimensional finite lane, the so--called residence time, is computed possibly in presence of a drift. A local inhomogeneity is introduced as a single defect site with jumping probabilities differing from those at all the other regular sites of the system. We find complex behaviors in the sense that the residence time is not monotonic as a function of some parameters of the model, such as the position of the defect site. In particular we show that introducing at suitable positions a defect opposing to the motion of the particles decreases the residence time, i.e., favors the flow of faster particles. The problem we study in this paper is strictly connected to the classical gambler's ruin problem, indeed, it can be thought as that problem in which the rules of the game are changed when the gambler's fortune reaches a particular a priori fixed value. The problem is approached both numerically, via Monte Carlo simulations, and analytically with two different techniques yielding different representations of the exact result