Stochastic Methods for the Neutron Transport Equation II: Almost sure growth.

The neutron transport equation (NTE) describes the flux of neutrons across a planar cross-section in an inhomogeneous fissile medium when the process of nuclear fission is active. Classical work on the NTE emerges from the applied mathematics literature in the 1950s through the work of R. Dautray and collaborators, [7, 8, 19]. The NTE also has a probabilistic representation through the semigroup of the underlying physical process when envisaged as a stochastic process; cf. [7, 17, 18, 20]. More recently, [6] and [16] have continued the probabilistic analysis of the NTE, introducing more recent ideas from the theory of spatial branching processes and quasi-stationary distributions. In this paper, we continue in the same vein and look at a fundamental description of stochastic growth in the supercritical regime. Our main result provides a significant improvement on the last known contribution to growth properties of the physical process in [20], bringing neutron transport theory in line with modern branching process theory such as [14, 12].Comment: one figur

Stochastic Methods for the Neutron Transport Equation I: Linear Semigroup asymptotics.

six figuresThe Neutron Transport Equation (NTE) describes the flux of neutrons through inhomogeneous fissile medium. Whilst well known in the post-Manhattan Project nuclear physics literature, cf. [11, 25, 27, 26, 23, 1, 36], the NTE has had a some- what scattered treatment in mathematical literature with a va- riety of different approaches. The rigorous treatment of Robert Dautray and collaborators, cf. [10, 9], firmly places the analysis of the NTE in the setting of classical c0-semigroup analysis of linear operators. Added to this, Mokhtar-Kharroubi [33] sum- marises the use of perturbation theory therein in order to un- derstand leading spectral properties of the NTE. Within a prob- abilistic framework, the NTE has received somewhat sporadic attention. Although the connection to probabilistic representa- tion has been understood since the early analysis of the NTE, see e.g. [34, 29, 37, 35, 9, 19], our aim is to reintroduce the NTE in the more modern context of Markov branching processes which describes the physical process of nuclear scattering and fission. Our presentation is thus, for the lesser part, a review of foun- dational material and, for the greater part, presentation of new research results. This paper is the first of a two-part instalment. In this first instalment we consider the Perron-Frobenius type decomposition of the linear semigroup associated to the NTE and the role it plays in the classical linear analysis of the un- derlying stochastic process. In the next instalment, we look at stochastic growth properties of the underlying physical process

The Effectiveness of Spiritual Wellness in the Classroom to Promote Resilience

The Effectiveness of Spiritual Wellness in the Classroom to Promote Resilience *Tori Horton, Emma Normand, Ben Smoot University of Montana, Missoula Abstract Spirituality is a crucial aspect of a child\u27s development but is often overlooked and misinterpreted in school settings. The purpose of this research study is to examine teachers’ approaches and activities in the classroom to foster students’ spiritual wellness and mental health. The current study is part of a larger project examining educators’ perspectives of social-emotional learning (SEL) and spirituality in the public-school setting. SEL has been suggested to cultivate spirituality in children leading to overall wellness. Public school teachers (N =12) were recruited using snowball sampling and interviewed using Zoom. Using qualitative methodology, we analyzed public school teachers\u27 perspectives on spirituality and approaches they used to support spiritual development in the classroom to promote resilience. Results revealed common themes related to yoga, nature, mindfulness, breathing exercises, and quiet time. Further, a recurring theme showed that participants expressed hesitancy and concern regarding potential pushback within the community related to teaching topics on spirituality. Several participants were able to link and identify similarities between both SEL and spirituality. Collaboration between teachers, administrators, and community members will help improve the integration of spirituality and support in the classroom for children

Stochastic Methods for Neutron Transport Equation III: Generational many-to-one and k_eff

The Neutron Transport Equation (NTE) describes the flux of neutrons over time through an inhomogeneous fissile medium. In the recent articles [5, 10], a probabilistic solution of the NTE is considered in order to demonstrate a Perron-Frobenius type growth of the solution via its projection onto an associated leading eigenfunction. In [9, 4], further analysis is performed to understand the implications of this growth both in the stochastic sense, as well as from the perspective of Monte-Carlo simulation. Such Monte-Carlo simulations are prevalent in industrial applications, in particular where regulatory checks are needed in the process of reactor core design. In that setting, however, it turns out that a different notion of growth takes centre stage, which is otherwise characterised by another eigenvalue problem. In that setting, the eigenvalue, sometimes called k-effective (written $k_\texttt{eff}$), has the physical interpretation as being the ratio of neutrons produced (during fission events) to the number lost (due to absorption in the reactor or leakage at the boundary) per typical fission event. In this article, we aim to supplement [5, 10, 9, 4], by developing the stochastic analysis of the NTE further to the setting where a rigorous probabilistic interpretation of keff is given, both in terms of a Perron-Frobenius type analysis as well as via classical operator analysis. To our knowledge, despite the fact that an extensive engineering literature and industrial Monte-Carlo software is concentrated around the estimation of keff and its associated eigenfunction, we believe that our work is the first rigorous treatment in the probabilistic sense (which underpins some of the aforesaid Monte-Carlo simulations)

A note on Riccati matrix difference equations

International audienceDiscrete algebraic Riccati equations and their fixed points are well understood and arise in a variety of applications, however, the time-varying equations have not yet been fully explored in the literature. In this article we provide a self-contained study of discrete time Riccati matrix difference equations. In particular, we provide a novel Riccati semigroup duality formula and a new Floquet-type representation for these equations. Due to the aperiodicity of the underlying flow of the solution matrix, conventional Floquet theory does not apply in this setting and thus further analysis is required. We illustrate the impact of these formulae with an explicit description of the solution of time-varying Riccati difference equations and its fundamental-type solution in terms of the fixed point of the equation and an invertible linear matrix map, as well as uniform upper and lower bounds on the Riccati maps. These are the first results of this type for time varying Riccati matrix difference equations