My paper on thermomechanical processes of charring wood is now published in Combustion And Flame. Here you can download the pdf for free for 50 days, if you are interested 🙂
In our study we develop a model for explaining the crack patterns which are formed on the wood surface when this is exposed to intense heat. It was believed for decades that such cracks are created by physicochemical processes like shrinkage, with impossibility to obtain an analytical model predicting their topology. On the contrary, we show that if one assumes the origin to be thermomechanical, the according analytical model can produce formulas which can describe and predict the crack patterns with an excellent agreement with the observations.
Here is the abstract:
In the assessment of wood charring, it was believed for a long time that physicochemical processes were responsible for the creation of cracking patterns on the charring wood surface. This implied no possibility to rigorously explain the crack topology. In this paper we show instead that below the pyrolysis temperatures, a primary global macro-crack pattern is already completely established by means of a thermomechanical instability phenomenon. First we report experimental observations of the crack patterns on orthotropic (wood) and isotropic (Medium Density Fibreboard) materials in inert atmosphere. Then we solve the 3D thermomechanical buckling problem numerically by using the Finite Element Method, and show that the different crack topologies can be explained qualitatively by the simultaneous thermal expansion and softening, taking into account the directional dependence of the elastic properties. Finally, we formulate a 2D model for a soft layer bonded to an elastic substrate, and find an equation predicting the inter-crack distance in the main crack-pattern for the orthotropic case. We also derive a formula for the critical thermal stress above which the plane surface will wrinkle and buckle. The results can be used for finding new ways to prevent or delay the crack formation, leading to improved fire safety of wood-based products.
I am now working with my colleagues on some developments of the model.
Thermal greetings to everybody!
My paper on theoretical modelling of daily hot water consumption in residential buildings is now published in Energy And Buildings. Here follows the abstract:
We consider Domestic Hot Water (DHW) consumption hourly data for Finnish apartments in November and August. Using datasets obtained in a previous work, we formulate a bottom-up model to quantify correlations in the consumption patterns, which are discerned by a different number of occupants for both weekday (WD) and weekend (WE). The analytical formulas thus obtained describe accurately the hourly consumption of any specific dataset. In particular, we can generate the consumption curves for unknown datasets and derive quantitatively the correlations between occupant groups and different seasons. We explain this procedure into details, define the key variables of the model and validate it against the measurements. Our quantitative results are immediately applicable to simulation tools for energy investigations and sizing of heating systems in Finland or areas with similar occupant behavior. More generally, the analytical, inductive method here introduced could be adapted to DHW studies concerning other geographic areas as well. We also argue that this simple, yet effective formalism might also be extended to other engineering contexts that are not strictly related to energy consumption. For example, the main idea could be developed and adapted to those disciplines where understanding dataset correlations constitutes an important investigation tool.
Analytical modelling and prediction formulas for domestic hot water consumption in residential Finnish apartments. Available from: https://www.researchgate.net/publication/309672534_Analytical_modelling_and_prediction_formulas_for_domestic_hot_water_consumption_in_residential_Finnish_apartments.
I will present these results in August, at the 7th International Symposium on Energy in Manchester: http://energy7.nscj.co.uk/
My latest paper in cosmology is now public! It took many years to write, as it was a single author side-project on a subject that is very different from my main field. My PhD was indeed in particle cosmology, while now I am mostly working on building physics and methods for energy saving in buildings. I am however still relatively active in theoretical physics, and this is meant to be the first article of a comeback into the field.
Here is the abstract:
In the framework of MSSM inflation, matter and gravitino production are here investigated through the decay of the fields which are coupled to the udd inflaton, a gauge invariant combination of squarks. After the end of inflation, the flat direction oscillates about the minimum of its potential, losing at each oscillation about 56\% of its energy into bursts of gauge/gaugino and scalar quanta when crossing the origin. These particles then acquire a large inflaton VEV-induced mass and decay perturbatively into the MSSM quanta and gravitinos, transferring the inflaton energy very efficiently via instant preheating.
Regarding thermalization, we show that the MSSM degrees of freedom thermalize very quickly, yet not immediately by virtue of the large vacuum expectation value of the inflaton, which breaks the SU(3)C×U(1)Y symmetry into a residual U(1). Compared to the case of LLe-type inflaton previously studied, we find an even more efficient energy transfer to the MSSM quanta, due to the enhanced particle content of the supersymmetric (SUSY) multiplet that is coupled to the flat direction. Full thermalization is achieved indeed after only O(40) oscillations.
We also compute the gravitino number density from the perturbative decay of the flat direction and of the SUSY multiplet. In agreement with the literature, the inflaton produces a negligible amount of gravitinos and does not raise any cosmological issues. On the contrary, the fields to which it is coupled are responsible for a severe gravitino overproduction problem, which is caused by their large VEV-induced effective masses. We argue that possible solutions might include non-coherent oscillations of multiple flat directions or fragmentation of the inflaton condensate with formation of Q-balls.
I’ve just posted a video of me playing the Celesti Alliance song “The Alliance” with my brand new Ibanez SR1405T (a wonderful instrument!). Straight into the amp and in passive mode, the signal chain is ridiculously simple: bass->cable-> Johnson Standard 30B amp. I didn’t even use my Seymour Duncan Studio Bass compressor, I wanted the sound of the instrument to come out as transparent as possible.
Of course, since the sound is recorded directly by the inbuilt mic of my camera, it is far from being Hi-Fi, but this gives the idea of how good this bass sounds even with low end gear, without any production.
Check it out and like it if you like!
*Bass rolls* I’m pleased to announce that I joined the Alliance! Celesti Alliance is an excellent heavy metal band, where I’ll be on bass duties with my loyal Jean Pierre.
Check the website and the songs from the EP Eagle’s Nest, those are really good tunes! The first gig will be very soon at Bar Rock Bear in Vantaa, on Sept 2nd. I’m actually learning the tracks and getting well into shape with my fingers, this will definitely be a good challenge for my stamina with fingerstyle 😀 I will keep a picture of Steve Harris in my bass case.
More dates (in Finland and abroad) are going to be confirmed soon, check my Live section for updates.
Here you see released on my Soundcloud the first recording for my solo project “Rock Me Amadeus”! It’s a robust rearrangement of some of Mozart’s immortal compositions, featuring extracts from Symphony n.25, Eine Kleine Nachtmusik and the Queen of the Night Aria.
I recorded all the strings (and also flutes, horns and oboes) with my electric guitars (Yamaha Pacifica 611HFM, RGX 521 and Hamer Californian).
A very challenging and instructive process, first of all tonewise but mostly because it didn’t reduce to merely playing some already written parts. Even for the comping it wasn’t always a one-to-one correspondence; for the lead guitar, I had to choose which instruments to transpose and, more importantly, how to provide the lead parts with a more personal rock/metal style.
It’s just a pity that the fully digital recording kills some of the dynamics.
The next track of the project will be Vivaldi’s Winter (first movement), hopefully ready by the end of 2016 (since I now joined the band Celesti Alliance on bass).
Very good news indeed. You can find a couple of my avantgarde tracks at https://quantumprana.bandcamp.com/