Ablation

Summary

Ablation (ablatio – removal) is the removal or destruction of something from an object by vaporization, chipping, erosive processes, or by other means. Examples of ablative materials are described below, including spacecraft material for ascent and atmospheric reentry, ice and snow in glaciology, biological tissues in medicine and passive fire protection materials. Artificial intelligence In artificial intelligence (AI), especially machine learning, ablation is the removal of a component of an AI system. The term is by analogy with biology: removal of components of an organism. Biology Biological ablation is the removal of a biological structure or functionality. Genetic ablation is another term for gene silencing, in which gene expression is abolished through the alteration or deletion of genetic sequence information. In cell ablation, individual cells in a population or culture are destroyed or removed. Both can be used as experimental tools, as in loss-of-

Official source

https://en.wikipedia.org/wiki/Ablation

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Numerical Simulations of the Apollo 4 Re-entry Trajectory

Ermioni Papadopoulou

Sample return capsules, as the Apollo Command Module have been widely used to ad- vance the knowledge and planning of manned lunar and planetary return missions. Such reentry vehicles undergo extreme thermal conditions, caused by shock-heated air during their super-orbital atmospheric re-entry. Such extreme conditions can result in failure of the aeroshell structure and loss of important payload. This technological challenge is ad- dressed by the use of ablative thermal protection systems (TPS), which dissipate the heat away from the vehicles front wall via ablative products release into the boundary layer. Additionally, such velocity and temperature magnitudes during reentry conditions intro- duce significant radiative heat loads, filling the shock layer with radiators that react with the ablative species injected by the capsule wall. Therefore, accurate numerical modeling techniques are required, so that the thermophys- ical, thermochemical environment of a reentry capsule can be successfully reproduced and predicted. The present work aims to numerically rebuild certain significant trajectory points, containing the peak heating points of the Apollo 4 terrestrial re-entry. This re- quires the coupling of the resolved flow-field with radiative and ablative effects in order to accurately predict the convective and radiative heat flux for each trajectory point. The results will be compared to previous calculations and existing flight data. The numerical simulations are performed in 2D thermal non-equilibrium with a compress- ible explicit Navier-Stokes solver, coupled to a radiation database and a thermal material response code to implement the ablative effects. The calculations are performed also in 3D, using a commercial implicit Navier-Stokes solver. The results will be used to reproduce the capsules trajectory and verify the accuracy of the associated Modeling Tools.

2014

The adipose tissue is increasingly recognized for the important role it plays in various diseases and pathological conditions, such as obesity, diabetes, cardiovascular diseases, osteoporosis, cancer, and aging. Despite its long-held reputation for being a simple fat storage tissue, we now know the adipose tissue is a singular organ playing a crucial role in whole-body metabolism and energy homeostasis. Understanding the development and functioning of adipose tissue and, in particular, of its structural and functional fat depots, is crucial to understanding human health and disease, and can pave the way for personalized therapeutic and preventive approaches. Transcription factors are key regulators of adipose tissue biogenesis, development, and responses to changes in environmental stimuli such as feeding, fasting, and exercise. The transcription repressor BCL6 - well known in immunology and cancer - has been recently linked to adipogenesis and metabolism. In the context of this thesis, in order to better understand the role of BCL6 in adipose tissue development and remodeling, we sought to further investigate the physiological function of BCL6 in white and brown adipose tissue. We developed and characterized a fat-specific conditional knockout mouse model for Bcl6 (Bcl6 FKO), and a Pdgfra-Cre driver was used to obtain in vivo ablation of Bcl6 in adipogenic precursors and stem cells (ASPCs). We discovered that ablation of Bcl6 in adipocyte precursors has a major impact on white fat mass and its distribution in the bodies of mice. Moreover, being fed a standard and a high-fat diet has a prominent effect on visceral adipose tissue, the mass of which was significantly reduced compared to that of control mice. Additionally, Bcl6 FKO mice did not demonstrate sensitivity to high-fat diet-induced mass gain and related comorbidities, such as hepatic steatosis and glucose-homeostasis alterations. The increased number of adipocytes observed in the gonadal adipose tissue occurred without increasing overall adiposity and body weight compared to control mice under a high-caloric diet regime. In conclusion, Bcl6 FKO mice represent a lean mouse model with a healthy balance between subcutaneous and visceral white adipose tissue depots. BCL6 could be an interesting adipose-specific target for therapeutic interventions in the context of obesity and related metabolic dysfunctions.

EPFL2019

Ground to Flight Investigations of Hayabusa with Ablation Effects

Nikhil Banerji, Elise Joy Fahy, Pénélope Leyland, Valentin Marguet, Jérémy Raphaël Mora-Monteros, Daniel Potter

Thermal protection systems (TPS) are of extreme importance for the survival of space vehicles especially during superorbital re-entry to Earth. The design of thermal protection systems requires in-depth knowledge of the thermal loading experienced during a re-entry. The thermal loading data is mostly determined using ground testing and can be backed up by modelling activities including computational fluid dynamics (CFD). The verification of this data with flight data is invaluable and a recent, rare example of an opportunity for comparison was the Hayabusa asteroid sample return mission, which landed in Australia in 2010. During this re-entry a team of international scientists collected spectral data which can now be used for comparison and verification of ground test and modelling/CFD data. Ground testing of subscale models at flight equivalent hypervelocity flow conditions (8 − 12 km/s) can be performed in hypersonic impulse facilities such as the X2 expansion tunnel at The University of Queensland. A recently developed method at The University of Queensland enables heated reinforced carbon-carbon (RCC) models to be tested at temperatures repre- sentative of those experienced in flight ( 2000 − 3000 K), in addition to testing with cold-wall metallic models. Hot wall testing allows more realistic simulation of re-entry flow characteristics including important thermal surface effects (surface chemistry, catalycity) which has previously not been possible. The eilmer3 compressible flow CFD code is used extensively for simulating atmospheric re-entry vehicles at flight and laboratory conditions. Simulations of the Hayabusa aeroshell incorporate heated walls, as well as surface catalycity, to accurately model the conditions experienced by the TPS. These simulations can be coupled with SACRAM, a 1D ablation modelling code, to include the effects of ablation and recession at critical points on the model surface. Current work is investigating the effects and validity of heat flux scaling correlations applied to a range of scaled models with the Hayabusa geometry and flight equivalent flow conditions. This will be achieved through results of CFD simulations, incorporating radiation and ablation modelling, and expansion tunnel testing with hot and cold wall models. Increased understand- ing of scaling methods will allow higher fidelity heat loading data to be acquired allowing more efficient and effective design of TPS. This paper will discuss results from CFD simulations coupled with ablation modelling and modelled surface chemistry. An outline of planned experiments in the X2 expansion tunnel, including background on the RCC heating method and condition development, will also be presented.

2013

EPFL2019

Ground to Flight Investigations of Hayabusa with Ablation Effects

Nikhil Banerji, Elise Joy Fahy, Pénélope Leyland, Valentin Marguet, Jérémy Raphaël Mora-Monteros, Daniel Potter

2013