Order in de Broglie - Bohm quantum mechanics

A usual assumption in the so-called {\it de Broglie - Bohm} approach to quantum dynamics is that the quantum trajectories subject to typical `guiding' wavefunctions turn to be quite irregular, i.e. {\it chaotic} (in the dynamical systems' sense). In the present paper, we consider mainly cases in which the quantum trajectories are {\it ordered}, i.e. they have zero Lyapunov characteristic numbers. We use perturbative methods to establish the existence of such trajectories from a theoretical point of view, while we analyze their properties via numerical experiments. Using a 2D harmonic oscillator system, we first establish conditions under which a trajectory can be shown to avoid close encounters with a moving nodal point, thus avoiding the source of chaos in this system. We then consider series expansions for trajectories both in the interior and the exterior of the domain covered by nodal lines, probing the domain of convergence as well as how successful the series are in comparison with numerical computations or regular trajectories. We then examine a H\'{e}non - Heiles system possessing regular trajectories, thus generalizing previous results. Finally, we explore a key issue of physical interest in the context of the de Broglie - Bohm formalism, namely the influence of order in the so-called {\it quantum relaxation} effect. We show that the existence of regular trajectories poses restrictions to the quantum relaxation process, and we give examples in which the relaxation is suppressed even when we consider initial ensembles of only chaotic trajectories, provided, however, that the system as a whole is characterized by a certain degree of order.Comment: 25 pages, 12 figure

Combining particle acceleration and coronal heating via data-constrained calculations of nanoflares in coronal loops

We model nanoflare heating of extrapolated active-region coronal loops via the acceleration of electrons and protons in Harris-type current sheets. The kinetic energy of the accelerated particles is estimated using semi-analytical and test-particle-tracing approaches. Vector magnetograms and photospheric Doppler velocity maps of NOAA active region 09114, recorded by the Imaging Vector Magnetograph (IVM), were used for this analysis. A current-free field extrapolation of the active-region corona was first constructed. The corresponding Poynting fluxes at the footpoints of 5000 extrapolated coronal loops were then calculated. Assuming that reconnecting current sheets develop along these loops, we utilized previous results to estimate the kinetic-energy gain of the accelerated particles and we related this energy to nanoflare heating and macroscopic loop characteristics. Kinetic energies of 0.1 to 8 keV (for electrons) and 0.3 to 470 keV (for protons) were found to cause heating rates ranging from $10^{-6}$ to 1 $\mathrm{erg\, s^{-1} cm^{-3}}$. Hydrodynamic simulations show that such heating rates can sustain plasma in coronal conditions inside the loops and generate plasma thermal distributions which are consistent with active region observations. We concluded the analysis by computing the form of X-ray spectra generated by the accelerated electrons using the thick target approach that were found to be in agreement with observed X-ray spectra, thus supporting the plausibility of our nanoflare-heating scenario.Comment: 11 figure

Quantum vortices and trajectories in particle diffraction

We investigate the phenomenon of the diffraction of charged particles by thin material targets using the method of the de Broglie-Bohm quantum trajectories. The particle wave function can be modeled as a sum of two terms $\psi=\psi_{ingoing}+\psi_{outgoing}$. A thin separator exists between the domains of prevalence of the ingoing and outgoing wavefunction terms. The structure of the quantum-mechanical currents in the neighborhood of the separator implies the formation of an array of \emph{quantum vortices}. The flow structure around each vortex displays a characteristic pattern called `nodal point - X point complex'. The X point gives rise to stable and unstable manifolds. We find the scaling laws characterizing a nodal point-X point complex by a local perturbation theory around the nodal point. We then analyze the dynamical role of vortices in the emergence of the diffraction pattern. In particular, we demonstrate the abrupt deflections, along the direction of the unstable manifold, of the quantum trajectories approaching an X-point along its stable manifold. Theoretical results are compared to numerical simulations of quantum trajectories. We finally calculate the {\it times of flight} of particles following quantum trajectories from the source to detectors placed at various scattering angles $\theta$, and thereby propose an experimental test of the de Broglie - Bohm formalism.Comment: 17 pages, 7 figures, accepted by IJB

Assessment of mould growth between elements of exterior constructions

The installation of external, internal or cavity wall insulation may be an efficient measure to reduce the energy consumption of a building. Applying internal wall insulation may be the only feasible solution for some cases. However, unintended consequences such as moisture accumulation within the building elements may occur. This study constitutes part of exploratory research which aimed to examine whether air sampling through impaction and culture-based analysis can be utilised for the assessment of mould growth within building elements. The present paper aims to determine whether the location of mould within confined spaces affects the sampling results. Towards this end, a CFD analysis was carried out and was complemented by two series of scale experiments. The results from both procedures were then compared and useful conclusions regarding the flow pattern and the potential relationship between the mould's location and the sampling results were extracted

Assessment of interstitial mould growth through impaction: a feasibility study

The application of insulation to solid walls is one of the measures to help reduce the energy consumption of a building. Where external wall insulation is not feasible (e.g. listed buildings), internal insulation may be the only option to improve the thermal property of external walls. However, such interventions may be followed by unintended consequences [1], such as moisture accumulation and the growth of mould [2]. The study aims to develop a method for the non-disruptive assessment of interstitial mould growth in internally insulated walls. Air sampling through impaction and culture-based analysis was used in the study. Mould species commonly found in buildings were cultivated and used in small-scale experiments, and the effects of several sampling periods and airflow rates assessed. Potential relationships between the sampling variables and the results were determined by means of statistical analysis - a strong correlation between the coverage of mould behind the wall and the sampling periods and airflow rates. The effect of the inertial impaction frequency on the sampling results and the feasibility and applicability of the suggested methodology in real-life scenarios are also discussed

The effect of the airflow pattern inside air gaps on the assessment of interstitial mould: A theoretical approach

Internal wall insulation is one of the few, possibly, the only feasible solution to efficiently reduce heat losses through the external walls of buildings where the application of external insulation is not an option, for example, in conservation areas. However, the application of this intervention may lead to unintended consequences, such as moisture accumulation and mould growth. Currently, no international standards and regulations exist to evaluate these hazards via non-destructive inspections. Air sampling through impaction and culture-based analysis was suggested in previous research as a potential non-disruptive methodology for interstitial mould testing. The method requires the perforation of the inner side of a wall and the creation of airflow through the operation of a pump, to allow the collection of particles from the confined space of interest. The present study aimed to assess the location of perforations and their effect on the airflow created and the airflow pattern variations due to changes in the airflow velocity at the outlet. Results regarding airflow features such as the turbulence intensity, dynamic pressure and volume-averaged velocity were also extracted and discussed. Practical application : The rapid changes in climate and net-zero emissions targets call for major improvements of the existing building stock towards a more sustainable future. The installation of internal wall insulation is one of the few and might be the only feasible solution for the efficient reduction of heat losses through uninsulated walls. However, this intervention might lead to moisture accumulation and thus moisture-related problems such as mould growth. This study aims to build upon previous work on interstitial mould growth assessment and contribute to the development of a well-defined testing protocol for building professionals

Mind the gap between non-activated (non-aggressive) and activated (aggressive) indoor fungal testing: impact of pre-sampling environmental settings on indoor air readings

Indoor fungal testing has been within the researchers’ scope of interest for more than a century. Various sampling and analysis techniques have been developed over the years, but no testing protocol has been yet standardised and widely accepted by the research and practitioner communities. The diversity in fungal taxa within buildings with varied biological properties and implications on the health and wellbeing of the occupants and the building fabric complicates the decision-making process for selecting an appropriate testing protocol. This study aims to present a critical review of non-activated and activated approaches to indoor testing, with an emphasis on the preparation of the indoor environment prior to sampling. The study demonstrates the differences in the outcomes of non-activated and activated testing through a set of laboratory experiments in idealised conditions and a case study. The findings suggest that larger particles are particularly sensitive to the sampling height and activation, and that non-activated protocols, despite dominating the current literature, can significantly underestimate the fungal biomass and species richness. Therefore, this paper calls for better-defined and activated protocols that can enhance robustness and reproducibility across the research domain focused on indoor fungal testing

Air sampling and analysis of indoor fungi : a critical review of passive (non- activated) and active (activated) sampling

For over a century, researchers have been concerned with what testing protocols to assess indoor fungi growth were most reliable. To that end, various sampling and analysis methods were developed. However, to present no testing procedure has been standardised. The vast number of different fungi species, the differences in their biological properties and their implications on the occupants’health and building fabric can make the decision-making process for an appropriate assessment protocol challenging. This research aims to make a critical review of passive (or nonactivated) and active (or activated) sampling and emphasize potential errors while interpreting results obtained from passive or active protocols

Developing a methodology to assess mould growth hidden behind internal wall insulation

Internal wall insulation is one of the few and possibly, the only feasible solution to efficiently reduce heat losses through the external walls of buildings where the application of external insulation is not an option, for example in conservation areas. However, the application of this intervention entails risks and may lead to unintended consequences, such as moisture accumulation and mould growth (1,2). Currently, no international standards and regulations exist to evaluate these hazards via nondestructive inspections. The present study aimed to design and propose a nondisruptive methodology for the assessment of mould growth in confined spaces such as air gaps and cavities within exterior constructions. The proposed method involved air sampling through impaction for the collection of data and culture-based techniques for their analysis

Developing a methodology to detect mould hidden behind internal wall insulation

Unintended consequences, such as mould growth, can occur in building constructions such as internally insulated walls. As part of exploratory research, we examined whether air sampling through impaction and culture-based analysis could be used as means to detect interstitial mould. The results extracted suggest that the measurements may be affected by the coverage of mould within confined spaces and the indoor air velocity