A Review of Supervised Machine Learning Applied to Ageing Research

Broadly speaking, supervised machine learning is the computational task of learning correlations between variables in annotated data (the training set), and using this information to create a predictive model capable of inferring annotations for new data, whose annotations are not known. Ageing is a complex process that affects nearly all animal species. This process can be studied at several levels of abstraction, in different organisms and with different objectives in mind. Not surprisingly, the diversity of the supervised machine learning algorithms applied to answer biological questions reflects the complexities of the underlying ageing processes being studied. Many works using supervised machine learning to study the ageing process have been recently published, so it is timely to review these works, to discuss their main findings and weaknesses. In summary, the main findings of the reviewed papers are: the link between specific types of DNA repair and ageing, ageing-related proteins tend to be highly connected and seem to play a central role in molecular pathways; ageing/longevity is linked with autophagy and apoptosis, nutrient receptor genes, and copper and iron ion transport. Additionally, several biomarkers of ageing were found by machine learning. Despite some interesting machine learning results, we also identified a weakness of current works on this topic: only one of the reviewed papers has corroborated the computational results of machine learning algorithms through wet-lab experiments. In conclusion, supervised machine learning has contributed to advance our knowledge and has provided novel insights on ageing, yet future work should have a greater emphasis in validating the predictions

Magnetic action on convection and heat transfer in ferrofluid

309-314The interplay of buoyancy and thermo-magnetic convection mechanisms are investigated in a horizontal ferrofluid layer heated from one wide side and cooled from another in the presence of external uniform transversal magnetic field. The influence of gravitational settling of magnetic particles and their aggregates on heat transfer and convection instability is also considered. The ferro-colloids with different concentrations of magnetic phase are employed for the control of driving magnetic forces. It is shown that in concentrated colloid the driving forces prevail over suppress ones, but in weak concentrated colloid the gradients of density due to gravity sedimentation of particles overwhelm convection stirring. It is important that thermo-magnetic convection mechanism allows strengthening of heat transfer in ferrofluid three times

Thermo-magneto-convective instabilities in a vertical layer of a ferro-magnetic fluid

We study convection in a vertical layer of ferro-magnetic fluid heated from the side and subject to a transverse magnetic field. It is found that the subse- quent fluid motion is caused by interacting thermo-gravitational and thermo- magnetic mechanisms. Our experiments and computations show that the excitation of magneto-convection leads to the formation of vertically aligned stationary rolls, while gravitational convection results in horizontal rolls cor- responding to a pair of counter-propagating thermal waves. The interaction of these instability modes leads to a wide spectrum of experimentally observed flow patterns including stationary rolls and standing waves of various spatial orientations. A comprehensive stability map is computed and compared with experimental flow visualisations. Disturbance energy is analysed to achieve a deeper insight into the physical mechanisms driving the fluid motion

Features of convection flows and heat transfer in magnetic colloids

Undertaken experimental observations and stability analysis have shown that a simple parallel buoyancy-induced flow in a differentially heated vertical layer of ferrofluid that is placed in an external uniform horizontal magnetic field is subject to a number of instabilities leading to the appearance of various convection patterns. Depending on the values of the governing parameters, the instability patterns are found to consist of vertical stationary magneto-convection rolls and/or vertically or obliquely counter-propagating thermo-gravitational or thermo-magnetic waves. Vertical rolls are the most prominent feature of the thermo-magnetic convection while inclined rolls and waves result from the interaction of the magnetic and gravitational mechanisms. Convective flow patterns are characterized by significantly increased heat transfer rates in comparison to pure conduction states. In particular, a significant intensification of an integral heat transfer was observed in convection regimes corresponding to vertical stationary rolls. It is found that these patterns are caused completely by a thermo-magnetic mechanism and are the consequence of an internal magnetic field gradient induced by the temperature dependence of fluid magnetization. These were not detected in earlier experiments and computations

Experimental study of initiation of convection in a spherical cavity filled with nanofluid

The stability of mechanical equilibrium in a spherical cavity filled with ferronanofluid heated from below is investigated experimentally. It is shown that when the temperature difference between the sphere poles is increased gradually the flow arises as a result of supercritical transition provided that nanofluid is well mixed before the start of the experiment. The subcritical transition from a motionless state arises if nanofluid remains at rest for a sufficiently long time (from one day to several weeks) prior to the experiment. The evolution of convection from a finite-amplitude excitation to a steady flow is described

Convective flows in magnetic nano-suspensions

Magnetic nano-suspensions (MNS) belong to one of the types of nano-fluids – colloid suspensions of single-domain particles with the average size of 10 nm. Two types of body forces arise in a non-uniformly magnetized non-conducting fluid placed in a magnetic field. First are the driving magnetic forces that can induce convective motion under certain conditions. The second type are the “resistive” forces which arise because of the distortion of a magnetic field due to the fluid motion. The magnetization non-uniformity in MNS can be caused by the temperature variation in the medium and by the non-uniformity of the volumetric distribution of magnetic particles. Therefore there exist two main mechanisms of magnetic convection: thermal and concentration-driven (magnetophoresis, thermophoresis). In addition, one has to take into account gravitational mechanisms of convection that also have two origins: thermal expansion and variation of concentration of a solid phase due to both the thermal diffusion and gravitational sedimentation of particles. It has been shown that convection in MNS is of an oscillatory type. Irregular oscillations were observed in one-, two- and tree-dimensional flows arising in a convection loop, spherical cavity and horizontal, inclined and vertical layers, respectively. A spontaneous excitation and decay of convection have been observed and regimes of chaotic localized states and of standing and propagating waves have been detected. The influence of longitudinal and transverse magnetic fields on the mechanical equilibrium and flows of fluid and the heat and mass transfer has been investigated. The interaction of thermo-magnetic and thermo-gravitational flows has been considered in order to determine the evolution of convective patterns. Understanding of the nature of magneto-convection is required for the use of MNS in such applications as energy conversion devices, various sensors, alternative cooling in micro-electronics and micro-gravitation and in crystal growth control

On convective instability of a vertical layer of magnetic colloid

Abstract not available in English