Renormalization group methods: Which kind of explanation?

Renormalization and Renormalization Group (RG) have proven to be very powerful tools in contemporary physics, with a decisive influence on how to conceive of key physical aspects, including theories themselves. While they can be tackled from a variety of standpoints, this paper focuses on a specific philosophical issue, that is, which kind of explanation can be provided by means of RG methods. After a short, historical overview to set out the physical context, we scrutinize recent debates on the topic, with a particular focus on Morrison's seminal work. With respect to her account, where RG explanation is portrayed as mathematical, non-reductive, and non-causal, our focus is on the first aspect. Our claim is that RG theory's explanatory role cannot reside exclusively in its mathematical character, independently from a physical interpretation: mathematical and physical features intersect in a highly non-trivial way to provide an explanation of physical phenomena.

Label-free near-infrared reflectance microscopy as a complimentary tool for two-photon fluorescence brain imaging.

In vivo two-photon imaging combined with targeted fluorescent indicators is currently extensively used for attaining critical insights into brain functionality and structural plasticity. Additional information might be gained from back-scattered photons from the near-infrared (NIR) laser without introducing any exogenous labelling. Here, we describe a complimentary and versatile approach that, by collecting the reflected NIR light, provides structural details on axons and blood vessels in the brain, both in fixed samples and in live animals under a cranial window. Indeed, by combining NIR reflectance and two-photon imaging of a slice of hippocampus from a Thy1-GFPm mouse, we show the presence of randomly oriented axons intermingled with sparsely fluorescent neuronal processes. The back-scattered photons guide the contextualization of the fluorescence structure within brain atlas thanks to the recognition of characteristic hippocampal structures. Interestingly, NIR reflectance microscopy allowed the label-free detection of axonal elongations over the superficial layers of mouse cortex under a cranial window in vivo. Finally, blood flow can be measured in live preparations, thus validating label free NIR reflectance as a tool for monitoring hemodynamic fluctuations. The prospective versatility of this label-free technique complimentary to two-photon fluorescence microscopy is demonstrated in a mouse model of photothrombotic stroke in which the axonal degeneration and blood flow remodeling can be investigated.