Neural networks : solving the chemistry of the interstellar medium

Non-equilibrium chemistry is a key process in the study of the interstellar medium (ISM), in particular the formation of molecular clouds and thus stars. However, computationally, it is among the most difficult tasks to include in astrophysical simulations, because of the typically high (>40) number of reactions, the short evolutionary time-scales (about 104 times less than the ISM dynamical time), and the characteristic non-linearity and stiffness of the associated ordinary differential equations system (ODEs). In this proof of concept work, we show that Physics Informed Neural Networks (PINN) are a viable alternative to traditional ODE time integrators for stiff thermochemical systems, i.e. up to molecular hydrogen formation (9 species and 46 reactions). Testing different chemical networks in a wide range of densities (−2 < log n/cm−3 < 3) and temperatures (1 < log T/K < 5), we find that a basic architecture can give a comfortable convergence only for simplified chemical systems: to properly capture the sudden chemical and thermal variations, a Deep Galerkin Method is needed. Once trained (∼103 GPUhr), the PINN well reproduces the strong non-linear nature of the solutions (errors ≲10 per cent⁠) and can give speed-ups up to a factor of ∼200 with respect to traditional ODE solvers. Further, the latter have completion times that vary by about ∼30 per cent for different initial n and T, while the PINN method gives negligible variations. Both the speed-up and the potential improvement in load balancing imply that PINN-powered simulations are a very palatable way to solve complex chemical calculation in astrophysical and cosmological problems

Dimensionless analysis of constrained damping treatments

One of the most effective ways of controlling vibrations in plate or beam structures is by means of constrained viscoelastic damping treatments. Contrary to the unconstrained configuration, the design of constrained and integrated layer damping treatments is multifaceted because the thickness of the viscoelastic layer acts distinctly on the two main counterparts of the strain energy the volume of viscoelastic material and the shear strain field. In this work, a parametric study is performed exploring the effect that the design parameters, namely the thickness/length ratio, constraining layer thickness, material modulus, natural mode and boundary conditions have on these two counterparts and subsequently, on the treatment efficiency. This paper presents five parametric studies, namely, the thickness/length ratio, the constraining layer thickness, material properties, natural mode and boundary conditions. The results obtained evidence an interesting effect when dealing with very thin viscoelastic layers that contradicts the standard treatment efficiency vs. layer thickness relation; hence, the potential optimisation of constrained and integrated viscoelastic treatments through the use of properly designed thin multilayer configurations is justified. This work presents a dimensionless analysis and provides useful general guidelines for the efficient design of constrained and integrated damping treatments based on single or multi-layer configurations. (C) 2012 Elsevier Ltd. All rights reserved

Double-duty actions for ending malnutrition within a decade

Malnutrition has many forms. Undernutrition can see children dangerously thin for their height (wasting), or their growth permanently impeded (stunting). Inadequate intake of key nutrients may weaken immune systems, impair brain development, and worsen the risk of conditions such as anaemia and blindness. Diets rich in calories well beyond the body's metabolic needs drive the burden of overweight and obesity, while excess dietary fat, sugar, and salt can increase the risks of non-communicable diseases (NCDs)

Exploitation of multi-objective optimization in retrofit analysis: a case study for the iron and steel production

Abstract Over the past few decades the issues related to the energy consumption and the climate change have been increased and they have achieved a significant position on the sustainability agenda of the steel industry. Steel production is among the largest energy-intensive industrial processes in the world, as well as one of the most important CO 2 emission sources. However, the major role of steel utilisation in the modern society is undeniable. The challenges of industrial energy systems aim at achieving CO 2 minimization, without neglecting energy efficiency as well as the development of effective models and strategies for process optimization. The application of Process Integration (PI) methods to the integrated steelmaking route, aims at achieving a reduction in the CO 2 emission by optimizing material and energy systems. The work presented in this paper is devoted to the development of a model for optimal exploitation of energy resources and by-products in integrated steelworks through application of multi-objective optimisation techniques. Cases of exploitation of the system within the management of the process gases are presented in a retrofit scenario and compared to the case of nominal operation

Overview of methods used to evaluate the adequacy of nutrient intakes for individuals and populations

The objective of the present paper is to review the methods of measuring micronutrient intake adequacy for individuals and for populations in order to ascertain best practice. A systematic review was conducted to locate studies on the methodological aspects of measuring nutrient adequacy. The results showed that for individuals, qualitative methods (to find probability of adequacy) and quantitative methods (to find confidence of adequacy) have been proposed for micronutrients where there is enough data to set an average nutrient requirement (ANR). If micronutrients do not have ANR, an adequate intake (AI) is often defined and can be used to assess adequacy, provided the distribution of daily intake over a number of days is known. The probability of an individual's intake being excessive can also be compared with the upper level of safe intake and the confidence of this estimate determined in a similar way. At the population level, adequacy can be judged from the ANR using the probability approach or its short cut – the estimated average requirement cut-point method. If the micronutrient does not have an ANR, adequacy cannot be determined from the average intake and must be expressed differently. The upper level of safe intake can be used for populations in a similar way to that of individuals. All of the methodological studies reviewed were from the American continent and all used the methodology described in the Institute of Medicine publications. The present methodology should now be adapted for use in Europe

Detecting brown adipose tissue activity with BOLD MRI in mice

The recent discovery of active brown adipose tissue (BAT) in adult humans and the correlation found between the activity of this tissue and resting metabolic rate strongly suggest that this tissue may be implicated in the development of obesity in humans, as it is in rodents. Despite the possible physiological role of this tissue in the onset of human obesity, few noninvasive imaging techniques to detect BAT activity in humans exist. The scope of this work is to investigate the possibility of detecting BAT activity using blood-oxygen-level-dependent MRI. Our results show that the strong increase in oxygen consumption and consequent increase in blood deoxyhemoglobin levels following BAT activation lead to a well-localized signal drop in BAT. This strongly suggests the possibility to use blood-oxygen-level-dependent MRI for the noninvasive detection of BAT activity