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)

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