Generalized Langevin Equation and non-Markovian fluctuation-dissipation theorem for particle-bath systems in external oscillating fields

The Generalized Langevin Equation (GLE) can be derived from a particle-bath Hamiltonian, in both classical and quantum dynamics, and provides a route to the (both Markovian and non-Markovian) fluctuation-dissipation theorem (FDT). All previous studies have focused either on particle-bath systems with time-independent external forces only, or on the simplified case where only the tagged particle is subject to the external time-dependent oscillatory field. Here we extend the GLE and the corresponding FDT for the more general case where both the tagged particle and the bath oscillators respond to an external oscillatory field. This is the example of a charged or polarisable particle immersed in a bath of other particles that are also charged or polarizable, under an external AC electric field. For this Hamiltonian, we find that the ensemble average of the stochastic force is not zero, but proportional to the AC field. The associated FDT reads as $\langle F_P(t)F_P(t')\rangle=mk_BT\nu(t-t')+(\gamma e)^2E(t)E(t')$, where $F_{p}$ is the random force, $\nu(t-t')$ is the friction memory function, and $\gamma$ is a numerical prefactor

Microscopic origin of nonlinear non-affine deformation and stress overshoot in bulk metallic glasses

The atomic theory of elasticity of amorphous solids, based on the nonaffine response formalism, is extended into the nonlinear stress-strain regime by coupling with the underlying irreversible many-body dynamics. The latter is implemented in compact analytical form using a qualitative method for the many-body Smoluchowski equation. The resulting nonlinear stress-strain (constitutive) relation is very simple, with few fitting parameters, yet contains all the microscopic physics. The theory is successfully tested against experimental data on metallic glasses, and it is able to reproduce the ubiquitous feature of stress-strain overshoot upon varying temperature and shear rate. A clear atomic-level interpretation is provided for the stress overshoot, in terms of the competition between the elastic instability caused by nonaffine deformation of the glassy cage and the stress buildup due to viscous dissipation.Comment: Physical Review B Rapid Comm., in pres

Theory of activated-rate processes under shear with application to shear-induced aggregation of colloids

Using a novel approximation scheme within the convective diffusion (two body Smoluchowski) equation framework, we unveil the shear-driven aggregation mechanism at the origin of structure-formation in sheared colloidal systems. The theory, verified against numerics and experiments, explains the induction time followed by explosive (irreversible) rise of viscosity observed in charge-stabilized colloidal and protein systems under steady shear. The Arrhenius-type equation with shear derived here, extending Kramers theory in the presence of shear, is the first analytical result clearly showing the important role of shear-drive in activated-rate processes as they are encountered in soft condensed matter

Shear banding in metallic glasses described by alignments of Eshelby quadrupoles

Plastic deformation of metallic glasses performed well below the glass transition temperature leads to the formation of shear bands as a result of shear localization. It is believed that shear banding originates from individual stress concentrators having quadrupolar symmetry. To elucidate the underlying mechanisms of shear band formation, microstructural investigations were carried out on sheared zones using transmission electron microscopy. Here we show evidence of a characteristic signature present in shear bands manifested in the form of sinusoidal density variations. We present an analytical solution for the observed post-deformation state derived from continuum mechanics using an alignment of quadrupolar stress field perturbations for the plastic events. Since we observe qualitatively similar features for three different types of metallic glasses that span the entire range of characteristic properties of metallic glasses, we conclude that the reported deformation behavior is generic for all metallic glasses, and thus has far-reaching consequences for the deformation behavior of amorphous solids in general

Single-molecule force spectroscopy with photoluminescent semiconducting polymers: Harnessing entropy

We discuss implications of a recent experimental breakthrough which uses a fluorescence-doped flexible semiconducting polymer to construct a single-molecule sensor which can detect ultra-weak forces in the molecular environment, with a grey scale down to 300 femtonewtons

“My dream to become somebody else”: The Dissociative Desire in Theodor Kallifatides’ The Past Is Not a Dream

Theodor Kallifatides’ autobiography, published in Greece in 2012 under the title Ta perasmena den einai oneiro (The past is not a dream) brings together in a single text many of the themes expressed in his literary works, and includes explicit and implicit references to his previous oeuvre. Taking into account René Girard’s literary theory of mimetic desire and Eve Kosofsky Sedgwick’s theory of homosocial desire, the paper offers a close reading of Ta perasmena den einai oneiro focused on the process of emancipation taking place in the book. Specifically, it explores the ways in which the subject-narrator uses the text and the writing process to describe and deconstruct his Greek masculinity and finally build a new gendered and national identity mediated by women, while at the same time re-writing his previous literary production in the light of his new self-awareness