Abrasion of flat rotating shapes

We report on the erosion of flat linoleum "pebbles" under steady rotation in a slurry of abrasive grit. To quantify shape as a function of time, we develop a general method in which the pebble is photographed from multiple angles with respect to the grid of pixels in a digital camera. This reduces digitization noise, and allows the local curvature of the contour to be computed with a controllable degree of uncertainty. Several shape descriptors are then employed to follow the evolution of different initial shapes toward a circle, where abrasion halts. The results are in good quantitative agreement with a simple model, where we propose that points along the contour move radially inward in proportion to the product of the radius and the derivative of radius with respect to angle

Scattering from Solutions of Star Polymers

We calculate the scattering intensity of dilute and semi-dilute solutions of star polymers. The star conformation is described by a model introduced by Daoud and Cotton. In this model, a single star is regarded as a spherical region of a semi-dilute polymer solution with a local, position dependent screening length. For high enough concentrations, the outer sections of the arms overlap and build a semi-dilute solution (a sea of blobs) where the inner parts of the actual stars are embedded. The scattering function is evaluated following a method introduced by Auvray and de Gennes. In the dilute regime there are three regions in the scattering function: the Guinier region (low wave vectors, q R << 1) from where the radius of the star can be extracted; the intermediate region (1 << q R << f^(2/5)) that carries the signature of the form factor of a star with f arms: I(q) ~ q^(-10/3); and a high wavevector zone (q R >> f^(2/5)) where the local swollen structure of the polymers gives rise to the usual q^(-5/3) decay. In the semi-dilute regime the different stars interact strongly, and the scattered intensity acquires two new features: a liquid peak that develops at a reciprocal position corresponding to the star-star distances; and a new large wavevector contribution of the form q^(-5/3) originating from the sea of blobs.Comment: REVTeX, 12 pages, 4 eps figure

Local correlation functional for electrons in two dimensions

We derive a local approximation for the correlation energy in two-dimensional electronic systems. In the derivation we follow the scheme originally developed by Colle and Salvetti for three dimensions, and consider a Gaussian approximation for the pair density. Then, we introduce an ad-hoc modification which better accounts for both the long-range correlation, and the kinetic-energy contribution to the correlation energy. The resulting functional is local, and depends parametrically on the number of electrons in the system. We apply this functional to the homogeneous electron gas and to a set of two-dimensional quantum dots covering a wide range of electron densities and thus various amounts of correlation. In all test cases we find an excellent agreement between our results and the exact correlation energies. Our correlation functional has a form that is simple and straightforward to implement, but broadly outperforms the commonly used local-density approximation

Valor e expressão do trabalho, do salário e do consumo entre mulheres operárias

When a former female manual worker decides to put on gel nails soon after losing the job that had prevented her from making up her hands (as someone in my fieldwork has recently done), it could be tempting to see a shift from a constrained worker identity to an unbound consumer identity materializing there. In the following pages, however, this episode and its local (and) labour context are taken as starting points to attempt a further exploration and a more nuanced understanding of the relationship between work and consumption. On theoretical and empirical grounds, it is argued that, instead of conceiving work and consumption as separate and indeed opposite realms, a close link between them – with work providing a relevant context to the working person as a consumer, and consumption providing subjects a relevant arena where to perform the value of their work – should be acknowledged and scrutinized.info:eu-repo/semantics/publishedVersio

Old corporate films and former factory workers: film reception as social memory

This article explores the seemingly compliant reception of old corporate films by former workers in a deindustrialized Portuguese town. The analysis identifies a particular, memory-focused mode of film reception among those workers, prompting joint consideration of convergent acquisitions from memory studies and film reception theory. This sheds light on the ways in which these workers reshape corporate film as their own relevant memory tool, the specific features of corporate film that support its memory value from a worker’s point of view, and the workers’ crafting, even so, of a lucid, class-bound relationship to the films as (corporate) discourse.info:eu-repo/semantics/publishedVersio

Spin filtering in nanowire directional coupler

The spin transport characteristics of a nanowire directional electronic coupler have been evaluated theoretically via a transfer matrix approach. The application of a gate field in the region of mixing allows for control of spin current through the different leads of the coupler via the Rashba spin-orbit interaction. The combination of spin-orbit interaction and applied gate voltages on different legs of the coupler give rise to a controllable modulation of the spin polarization. Both structural factors and field strength tuning lead to a rich phenomenology that could be exploited in spintronic devices.Comment: 9 pages, 4 figure

Construction of the B88 exchange-energy functional in two dimensions

We construct a generalized-gradient approximation for the exchange-energy density of finite two-dimensional systems. Guided by non-empirical principles, we include the proper small-gradient limit and the proper tail for the exchange-hole potential. The observed performance is superior to that of the two-dimensional local-density approximation, which underlines the usefulness of the approach in practical applications