Anisotropic plastic deformation by viscous flow in ion tracks

A model describing the origin of ion beam-induced anisotropic plastic deformation is derived and discussed. It is based on a viscoelastic thermal spike model for viscous flow in single ion tracks derived by Trinkaus and Ryazanov. Deviatoric (shear) stresses, brought about by the rapid thermal expansion of the thermal spike, relax at ion track temperatures beyond a certain flow temperature. Shear stress relaxation is accompanied by the generation of viscous strains. The model introduces differential equations describing the time evolution of the radial and axial stresses, enabling an exact derivation of the viscous strains for any ion track temperature history T(t). It is shown that the viscous strains effectively freeze in for large track cooling rates, whereas reverse viscous flow reduces the net viscous strains in the ion track for smaller cooling rates. The model is extended to include finite-size effects that occur for ion tracks close to the sample edge, enabling a comparison with experimental results for systems with small size. The "effective flow temperature approach" that was earlier introduced by Trinkaus and Ryazanov by making use of Eshelby's theory of elastic inclusions, follows directly from the viscoelastic model as a limiting case. We show that the viscous strains in single ion tracks are the origin of the macroscopic anisotropic deformation process. The macroscopic deformation rate can be directly found by superposing the effects of single ion impacts. By taking realistic materials parameters, model calculations are performed for experimentally studied cases. Qualitative agreement is observed

Three-dimensional cross-linked F-actin networks:Relation between network architecture and mechanical behavior

Numerical simulations are reported for the response of three-dimensional cross-linked F-actin networks when subjected to large deformations. In addition to the physiological parameters such as actin and cross-linker concentration, the model explicitly accounts for filament properties and network architecture. Complementary to two-dimensional studies, we find that the strain-stiffening characteristics depend on network architecture through the local topology around cross-links

The origin of stiffening in cross-linked semiflexible networks

Strain stiffening of protein networks is explored by means of a finite strain analysis of a two-dimensional network model of cross-linked semiflexible filaments. The results show that stiffening is caused by non-affine network rearrangements that govern a transition from a bending dominated response at small strains to a stretching dominated response at large strains. Thermally-induced filament undulations only have a minor effect; they merely postpone the transition.Comment: 5 pages, 5 figure

Waarom laten mensen toeslagen liggen?

Sociale voorzieningen zoals toeslagen bieden inkomenszekerheid aan financieel kwetsbarehuishoudens. Toch vraagt lang niet iedereen deze voorzieningen aan. Om te achterhalen hoe ditkomt, namen we een vragenlijst af bij meer dan 700 Nederlanders die recht hebben op zorgtoeslagen gingen we de straat op om mensen te interviewen die moeten rondkomen van weinig geld.Social decision makin

The role of financial stress in mental health changes during COVID-19

Using longitudinal data before and during the first six months of the COVID-19 pandemic for a representative sample of Dutch households, we examined the role of financial stress, defined as the subjective experience of lacking financial resources to cope with demands, in mental health changes. Also, we examined financial stress and mental health relations with households’ income, savings, and debts. The data revealed that average mental health did not change during the first six months of the pandemic but showed considerable underlying heterogeneity. Results showed that financial stress changes significantly explained this heterogeneity. Increases in financial stress predicted decreases in mental health, whereas decreases in financial stress predicted increases in mental health. While income did not explain financial stress changes, fewer savings and more debts were related to increased financial stress, which was, in turn, negatively related to mental health. We discuss the implications of our findings for mental health care and financial security policy and provide suggestions for future research.Social decision makin

Social security or insecurity? The experience of welfare participation by financially vulnerable households in the Netherlands

Social welfare aims to support financially vulnerable households by protecting them from financial shocks and providing them with a basic standard of living. Many eligible households, however, do not take up social welfare. We present the results of in-depth interviews with 31 members of financially vulnerable households in two large Dutch cities about their experiences with welfare. We examined the role of money in their lives, what inhibited them from taking up social welfare, and how they sought support. For many interviewed households, money was a source of stress. The fear of reclaims and mistrust of government institutions were the main inhibitors to participating in welfare programs. Whereas the experience of shame and stigma were substantial inhibitors for claiming local welfare benefits, they were not for participating in national welfare programs. Formal and informal help promoted welfare participation, but many participants lacked access to both. We discuss policies that could decrease the perceived uncertainty of benefits receipt and give directions for future research.Social decision makin

How executive functioning and financial self-efficacy predict subjective financial well-being via positive financial behaviors

Social decision makin