Shear modulus of simulated glass-forming model systems: Effects of boundary condition, temperature and sampling time

The shear modulus G of two glass-forming colloidal model systems in d=3 and d=2 dimensions is investigated by means of, respectively, molecular dynamics and Monte Carlo simulations. Comparing ensembles where either the shear strain gamma or the conjugated (mean) shear stress tau are imposed, we compute G from the respective stress and strain fluctuations as a function of temperature T while keeping a constant normal pressure P. The choice of the ensemble is seen to be highly relevant for the shear stress fluctuations mu_F(T) which at constant tau decay monotonously with T following the affine shear elasticity mu_A(T), i.e. a simple two-point correlation function. At variance, non-monotonous behavior with a maximum at the glass transition temperature T_g is demonstrated for mu_F(T) at constant gamma. The increase of G below T_g is reasonably fitted for both models by a continuous cusp singularity, G(T) is proportional to (1-T/T_g)^(1/2), in qualitative agreement with some recent replica calculations. It is argued, however, that longer sampling times may lead to a sharper transition. The additive jump discontinuity predicted by mode-coupling theory and other replica calculations thus cannot ultimately be ruled out

Note: Scale-free center-of-mass displacement correlations in polymer films without topological constraints and momentum conservation

We present here computational work on the center-of-mass displacements in thin polymer films of finite width without topological constraints and without momentum conservation obtained using a well-known lattice Monte Carlo algorithm with chain lengths ranging up to N=8192. Computing directly the center-of-mass displacement correlation function C_N(t) allows to make manifest the existence of scale-free colored forces acting on a reference chain. As suggested by the scaling arguments put forward in a recent work on three-dimensional melts, we obtain a negative algebraic decay C_N(t) \sim -1/(Nt) for times t << T_N with T_N being the chain relaxation time. This implies a logarithmic correction to the related center-of-mass mean square-displacement h_N(t) as has been checked directly

Scale-free center-of-mass displacement correlations in dense polymer solutions and melts without topological constraints and momentum conservation: A bond-fluctuation model study

By Monte Carlo simulations of a variant of the bond-fluctuation model without topological constraints we examine the center-of-mass (COM) dynamics of polymer melts in $d=3$ dimensions. Our analysis focuses on the COM displacement correlation function \CN(t) \approx \partial_t^2 \MSDcmN(t)/2, measuring the curvature of the COM mean-square displacement \MSDcmN(t). We demonstrate that \CN(t) \approx -(\RN/\TN)^2 (\rhostar/\rho) \ f(x=t/\TN) with $N$ being the chain length ($16 \le N \le 8192$), \RN\sim N^{1/2} the typical chain size, \TN\sim N^2 the longest chain relaxation time, $\rho$ the monomer density, \rhostar \approx N/\RN^d the self-density and $f(x)$ a universal function decaying asymptotically as $f(x) \sim x^{-\omega}$ with $\omega = (d+2) \times \alpha$ where $\alpha = 1/4$ for $x \ll 1$ and $\alpha = 1/2$ for $x \gg 1$. We argue that the algebraic decay N \CN(t) \sim - t^{-5/4} for t \ll \TN results from an interplay of chain connectivity and melt incompressibility giving rise to the correlated motion of chains and subchains.Comment: 27 pages, 12 figure

Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distribution

The larger number of models of asteroid shapes and their rotational states derived by the lightcurve inversion give us better insight into both the nature of individual objects and the whole asteroid population. With a larger statistical sample we can study the physical properties of asteroid populations, such as main-belt asteroids or individual asteroid families, in more detail. Shape models can also be used in combination with other types of observational data (IR, adaptive optics images, stellar occultations), e.g., to determine sizes and thermal properties. We use all available photometric data of asteroids to derive their physical models by the lightcurve inversion method and compare the observed pole latitude distributions of all asteroids with known convex shape models with the simulated pole latitude distributions. We used classical dense photometric lightcurves from several sources and sparse-in-time photometry from the U.S. Naval Observatory in Flagstaff, Catalina Sky Survey, and La Palma surveys (IAU codes 689, 703, 950) in the lightcurve inversion method to determine asteroid convex models and their rotational states. We also extended a simple dynamical model for the spin evolution of asteroids used in our previous paper. We present 119 new asteroid models derived from combined dense and sparse-in-time photometry. We discuss the reliability of asteroid shape models derived only from Catalina Sky Survey data (IAU code 703) and present 20 such models. By using different values for a scaling parameter cYORP (corresponds to the magnitude of the YORP momentum) in the dynamical model for the spin evolution and by comparing synthetics and observed pole-latitude distributions, we were able to constrain the typical values of the cYORP parameter as between 0.05 and 0.6.Comment: Accepted for publication in A&A, January 15, 201

Scale-free static and dynamical correlations in melts of monodisperse and Flory-distributed homopolymers: A review of recent bond-fluctuation model studies

It has been assumed until very recently that all long-range correlations are screened in three-dimensional melts of linear homopolymers on distances beyond the correlation length $\xi$ characterizing the decay of the density fluctuations. Summarizing simulation results obtained by means of a variant of the bond-fluctuation model with finite monomer excluded volume interactions and topology violating local and global Monte Carlo moves, we show that due to an interplay of the chain connectivity and the incompressibility constraint, both static and dynamical correlations arise on distances $r \gg \xi$. These correlations are scale-free and, surprisingly, do not depend explicitly on the compressibility of the solution. Both monodisperse and (essentially) Flory-distributed equilibrium polymers are considered.Comment: 60 pages, 49 figure

Scaling slowly rotating asteroids with stellar occultations

Context. As evidenced by recent survey results, the majority of asteroids are slow rotators (spin periods longer than 12 h), but lack spin and shape models because of selection bias. This bias is skewing our overall understanding of the spins, shapes, and sizes of asteroids, as well as of their other properties. Also, diameter determinations for large (>60 km) and medium-sized asteroids (between 30 and 60 km) often vary by over 30% for multiple reasons. Aims. Our long-term project is focused on a few tens of slow rotators with periods of up to 60 h. We aim to obtain their full light curves and reconstruct their spins and shapes. We also precisely scale the models, typically with an accuracy of a few percent. Methods. We used wide sets of dense light curves for spin and shape reconstructions via light-curve inversion. Precisely scaling them with thermal data was not possible here because of poor infrared datasets: large bodies tend to saturate in WISE mission detectors. Therefore, we recently also launched a special campaign among stellar occultation observers, both in order to scale these models and to verify the shape solutions, often allowing us to break the mirror pole ambiguity. Results. The presented scheme resulted in shape models for 16 slow rotators, most of them for the first time. Fitting them to chords from stellar occultation timings resolved previous inconsistencies in size determinations. For around half of the targets, this fitting also allowed us to identify a clearly preferred pole solution from the pair of two mirror pole solutions, thus removing the ambiguity inherent to light-curve inversion. We also address the influence of the uncertainty of the shape models on the derived diameters. Conclusions. Overall, our project has already provided reliable models for around 50 slow rotators. Such well-determined and scaled asteroid shapes will, for example, constitute a solid basis for precise density determinations when coupled with mass information. Spin and shape models in general continue to fill the gaps caused by various biases

O componente curricular libras na percepção das acadêmicas dos cursos de pedagogia e psicopedagogia do Unilasalle – Canoas/RS

Submitted by Leila Silva ([email protected]) on 2018-08-01T18:45:26Z No. of bitstreams: 1 Carlos roberto martins.pdf: 791350 bytes, checksum: c082a9917b5c44d2f1a49220d4342631 (MD5)Made available in DSpace on 2018-08-01T18:45:26Z (GMT). No. of bitstreams: 1 Carlos roberto martins.pdf: 791350 bytes, checksum: c082a9917b5c44d2f1a49220d4342631 (MD5) Previous issue date: 2009This research aims at the perception of academics of Pedagogy and Psychoeducation of the Centro Universitário La Salle – UNILASALLE – Canoas/RS on the curricular component LIBRAS (Brazilian Signs Language), which was introduced in 2008 in the curricula of these courses by the Decree 5.626 of 22 December 2005. Therefore, the research shows the entire historical context of origin of Sign Language till its formalization and compulsory inclusion in the curricula of higher education and more specifically some interfaces of pedagogic situations in UNILASALLE. The research was conducted from a semi-structured interview consisting of ten questions through a qualitative and participant research, while it was established a communicative relationship with the academics and interacting by a filmed interview providing a reciprocal relationship between the interviewer and the interviewed. The survey was conducted in a qualitative way and from this interview it was done an evaluation of responses, with the idea not only to describe, but to reflect on what has been described. The research is relevant and important because it deals with the insertion of LIBRAS as a curriculum component, which is a new situation in academia. The perspective was to seek answers about the teaching practice component of LIBRAS promoting reflection on its teaching in courses in Higher Education.A presente investigação objetiva apresentar a percepção das acadêmicas dos Cursos de Pedagogia e Psicopedagogia do Centro Universitário La Salle – UNILASALLE – Canoas/RS sobre o componente curricular de Libras, que pela exigência do Decreto 5.626 de 22 de Dezembro de 2005, foi inserido em 2008 nos currículos destes Cursos. Para tanto, a investigação mostra todo o contexto histórico de origem da Língua de sinais até sua oficialização e inserção obrigatória nos currículos do ensino superior e mais especificamente algumas interfaces de natureza pedagógica sobre o contexto do UNILASALLE. A investigação foi realizada a partir de uma entrevista semi-estruturada composta de dez questões, através de uma pesquisa qualitativa e participante, visto que foi estabelecida uma relação comunicativa com as acadêmicas, e uma interação em entrevista filmada proporcionando uma relação recíproca entre quem pergunta e quem responde. A investigação–ação partiu de entrevistas em que as respostas foram descritas e analisadas. São cinco capítulos incluindo introdução e conclusão. A partir do capítulo dois da pesquisa aparece uma trajetória histórica sobre as lutas e conquistas dos surdos quanto ao uso da língua de sinais no mundo desde a antiguidade, mostrando movimentos e mudanças que marcaram época na sociedade especialmente na educação. No capítulo três é apresentada a história do UNILASALLE, tratando especificamente dos cursos de Pedagogia e Psicopedagogia, expondo a matriz curricular e as propostas pedagógicas de cada curso visualizando a inserção do componente curricular de Libras nesses cursos. No capítulo quatro estão as descrições e as análises das entrevistas realizadas com dezesseis acadêmicas dos cursos de Pedagogia e Psicopedagogia, tratando sobre o componente curricular de Libras. Também há um diálogo filmado que foi descrito para complementar a pesquisa