Mathematical modelling of the solidification of liquid tin with electromagnetic stirring

It is well known that during alloy solidification, convection currents close to the so-lidification front have an influence on the structure of dendrites, the local solute concentration, the pattern of solid segregation, and eventually the microstructure of the casting and hence its mechanical properties. Controlled stirring of the melt in continuous casting or in ingot solidification is thought to have a beneficial effect. Free convection currents occur naturally due to temperature differences in the melt and for any given configuration, their strength is a function of the degree of superheat present. A more controlled forced convection current can be induced using electro-magnetic stirring. The authors have applied their Control-Volume based MHD method [1, 2] to the problem of tin solidification in an annular crucible with a water-cooled inner wall and a resistance heated outer one, for both free and forced convection situations and for various degrees of superheat. This problem was studied experimentally by Vives and Perry [3] who obtained temperature measurements, front positions and maps of electro-magnetic body force for a range of superheat values. The results of the mathematical model are compared critically against the experimental ones, in order to validate the model and also to demonstrate the usefulness of the coupled solution technique followed, as a predictive tool and a design aid. Figs 6, refs 19.

Modeling the dynamics of Magnetic Semilevitation Melting

In semilevitation melting, a cylindrical metal ingot is melted by a coaxial a.c. induction coil. A watercooled solid base supports the ingot, while the top and side free surface is confined by the magnetic forces as the melting front progresses. The dynamic interplay between gravity, hydrodynamic stress, and the Lorentz force in the fluid determines the instantaneous free surface shape. The coupled nonstationary equations for turbulent flow, heat with phase change, and high-frequency electromagnetic field are solved numerically for the axisymmetric time-dependent domain by a continuous mesh transformation, using a pseudospectral method. Results are obtained for the two actually existing coil configurations and several validation cases.

Multiscale modeling of the onset of freckle formation during vacuum arc remelting

A multiscale model for the Vacuum Arc Remelting process (VAR) was developed to simulate dendritic microstructures during solidification and investigate the onset of freckle formation. On the macroscale, a 3D multi-physics model of VAR was used to study complex physical phenomena, including liquid metal flow with turbulence, heat transfer, and magnetohydrodynamics. The results showed that unsteady fluid flow in the liquid pool caused significant thermal perturbation at the solidification front. These results were coupled into a micromodel to simulate dendritic growth controlled by solute diffusion, including local remelting. The changes in Rayleigh number as the microstructure remelts was quantified to provide an indicator of when fluid flow channels (i.e. freckles) will initiate in the mushy zone. By examining the simulated microstructures, it was found that the Rayleigh number increased more than 300 times during remelting, which suggests that thermal perturbation could be responsible for the onset of freckle formation.

Adult personality inconsistency and problems with parents: uncovering the roots of the false self

Research has established that individuals who tend to vary their personality depending on who they are with, show a variety of signs of psychological maladjustment in comparison to those who do not; they show more negative affect (Baird, Le and Lucas, 2006), lower life satisfaction (Suh, 2002), lower self-esteem (Sheldon et al., 1997), lower role-satisfaction (Donahue et al., 1993), higher rates of depression (Lutz and Ross, 2003), more anxiety (Diehl, Hastings and Stanton, 2001) and poorer physical health (Cross, Gore and Morris, 2003). It has also been shown that personality variability is positively related to the experience of inauthenticity and falsity (Sheldon et al., 1997). Donahue, Roberts, Robins and John (1993) found that personality inconsistency of this type is related to tension within the family. Psychoanalytic theory has also linked the operation of an adult false self to experiences with parents, particularly in early life (Winnicott, 1960). It was hypothesized that personality variability and the adult experience of falsity in social situations would be related to an emotionally unstable relationship with parents. The method to test this comprised a questionnaire-based survey given to a non-clinical population. The final sample comprised 305, with 193 women and 112 men, aged from 19 to 55. The first questionnaire asked participants to rate personality traits, including emotional stability, in three social contexts - with parents, with friends and with work colleagues. The second part involved 3 questions; participants were asked to select in which of the aforementioned three social contexts they felt “most themselves”; in which they were “most authentic” and in which they “put on a front”. It was found, consistent with predictions, that an index of overall personality variability calculated from the personality questionnaire correlated strongly with emotional instability around parents (r = 0.46, p<0.001), while not correlating with emotional instability in either of the other two contexts measured. This suggests a specific link between a person’s relationship with their parents and their overall personality integration. Furthermore, it was found that participants who cited one of the three social contexts (parents, friends, work colleagues) as being one in which they were “more themselves” or “more authentic” had significantly higher ratings of emotional instability with parents than those participants who found that they were equally authentic across settings (F = 9.8, p<0.005). The results suggest a clear link between a person’s relationships with their parents and their adult personality integration. An explanation is that individuals who experience an anxious or ambiguous attachment with their parents in childhood may fear rejection or abandonment in later life, and so habitually adapt their personality to fit in to social contexts as adults, in order to be accepted by others and to minimize the possibility of social rejection. These individuals meanwhile retain an emotionally unstable relationship with their parents in adulthood. This interpretation is speculative but is open to empirical testing. Clinicians should be aware that attachment problems with parents may underlie poor personality integration in adulthood.