Polymer indentation with mesoscopic molecular dynamics

Indentation tests are used to determine the hardness of a material, e.g., Rockwell, Vickers, or Knoop. The indentation process is empirically observed in the laboratory during these tests; the mechanics of indentation is insufficiently understood. We have performed first molecular dynamics computer simulations of indentation resistance of polymers with a chain structure similar to that of high density polyethylene (HDPE). A coarse grain model of HDPE is used to simulate how the interconnected segments respond to an external force imposed by an indenter. Results include the time-dependent measurement of penetration depth, recovery depth, and recovery percentage, with respect to indenter force, indenter size, and indentation time parameters. The simulations provide results that are inaccessible experimentally, including continuous evolution of the pertinent tribological parameters during the entire indentation process.

Molecular dynamics computer simulation of scratch resistance testing of polymers: visualization

Experimental scratch resistance testing provides two numbers: the penetration depth Rp and the healing depth Rh. In molecular dynamics computer simulations, we create a material consisting of N statistical chain segments by polymerization; a reinforcing phase can be included. Then we simulate the movement of an indenter and response of the segments during X time steps. Each segment at each time step has three Cartesian coordinates of position and three of momentum. We describe methods of visualization of results based on a record of 6NX coordinates. We obtain a continuous dependence on time t of positions of each of the segments on the path of the indenter. Scratch resistance at a given location can be connected to spatial structures of individual polymeric chains.

Simulating scratch behavior of polymers with mesoscopic molecular dynamics

Part replacement and repair is needed in structures with moving parts because of scratchability and wear. In spite of some accumulation of experimental evidence, scratch resistance is still not well understood. We have applied molecular dynamics to study scratch resistance of amorphous polymeric materials through computer simulations. As a first approach, a coarse grain model was created for high density polyethylene at the mesoscale. We have also extended the traditional approach and used real units rather than reduced units (to our knowledge, for the first time), which enable an improved quantification of simulation results. The obtained results include analysis of penetration depth, residual depth and recovery percentage related to indenter force and size. Our results show there is a clear effect from these parameters on the tribological properties. We also discuss a "crooked smile" effect on the scratched surface and the reasons for its appearance.

Pectus Excavatum postsurgical outcome based on preoperative soft body dynamics simulation

Pectus excavatum is the most common congenital deformity of the anterior chest wall, in which an abnormal formation of the rib cage gives the chest a caved-in or sunken appearance. Today, the surgical correction of this deformity is carried out in children and adults through Nuss technic, which consists in the placement of a prosthetic bar under the sternum and over the ribs. Although this technique has been shown to be safe and reliable, not all patients have achieved adequate cosmetic outcome. This often leads to psychological problems and social stress, before and after the surgical correction. This paper targets this particular problem by presenting a method to predict the patient surgical outcome based on pre-surgical imagiologic information and chest skin dynamic modulation. The proposed approach uses the patient pre-surgical thoracic CT scan and anatomical-surgical references to perform a 3D segmentation of the left ribs, right ribs, sternum and skin. The technique encompasses three steps: a) approximation of the cartilages, between the ribs and the sternum, trough b-spline interpolation; b) a volumetric mass spring model that connects two layers - inner skin layer based on the outer pleura contour and the outer surface skin; and c) displacement of the sternum according to the prosthetic bar position. A dynamic model of the skin around the chest wall region was generated, capable of simulating the effect of the movement of the prosthetic bar along the sternum. The results were compared and validated with patient postsurgical skin surface acquired with Polhemus FastSCAN system

Exploring the interdisciplinary process in design education

The work presented herein follows an ongoing research that aims to analyze methodological practices to be applied in Design Education. A reflection about methodological strategies in Design Education and the function of drawing in Design represents the beginning of this study. Then, we developed an interdisciplinary pedagogical experience with the Graphic Design 1st grade students from our institution (IPCA). In the current academic year, 2013/2014, we continue to evolve this project, introducing changes in the initial proposal. Major alterations focused on the aspects that could be strengthened in terms of interdisciplinarity. In this article, the authors describe those changes and discuss the outcomes of the novel proposal. As we have already reported, this investigation follows a reflection about working methods to be adopted in Design Education. This is in accordance with other previously published works that purpose the enlargement of Design into new knowledge fields such as Experience or Service Design, changing not only the role of the graphic designer, but also the skills required to be a professional designer (Alain Findelli, 2001), (Brian Lawson, 2006), (Ciampa-Brewer, 2010). Furthermore, concepts such as cooperation or multidisciplinary design, amongst others, have been frequently debated as design teaching strategies (Heller and Talarico, 2011, pp. 82-85). These educational approaches also have an impact on our research. The analysis of all these authors’ contributions together with a reflection on our teaching practice allowed us to propose an improved interdisciplinary intervention.

The strategic management of creation process and of change: a theoretical contribute from the perspective of tourism

The entrepreneurship and innovation have been gradually gaining ground in the academic community as a field of study. However, the interpretations surrounding fragmented, without a univocal definition. In last decades, tourism has received greater attention from researchers in various sciences, varying only by the different emphases considered: economic, social, cultural and environmental. As other emerging sectors in a modern economy, tourism is a dynamic and ever-changing industry. The study has as purpose to provide a better understanding regarding the essence of entrepreneurship: theoretical and practical implications from the perspective of tourism. Regarding the methodology used here, this is a conceptual paper with a literature review that brings together the major components of entrepreneurship and its implications tourist perspective and conceptual model of the dynamic nature of the Triggering Process and innovation (e.g. iTravey, Interactive Stores, Tourist Transportable Tower).

The international harmonization process of public accounting in Portugal: the perspective of different stakeholders

This paper investigates the reform of public accounting in Portugal through the IPSAS adoption highlighting the perception of different stakeholders. Two competing theories (NPM and the institutional theory) are used to understand public accounting changes within the Portuguese context. In general, different stakeholders agree with the favorable moment and the context of the reform. The context of financial crises and the great external pressures to cut public deficits and to improve the quality of financial information seem to be the most important factors to stimulate changes in public accounting. In addition, stakeholders recommend the use of different strategies to ensure success.

The internationally standardized process of public accounting: the perspective of different stakeholders in Portugal

New Public Management (NPM) led to great pressures for to introduce and adapt businesslike accounting in the public sector (Hood, 1995; Lapsley, 2008; Lapsley et al., 2009), specially the transition from cash basis to accrual-based accounting. In consequence, since the last 20 years we assist to a movement towards internationally standardized of public sector accounting that led to the publication of 32 International Public Sector Accounting Standards (IPSAS) for all public sector entities from national central governments to local governments (IFAC, 2008). These standards are accrual-basis and they emphasize the balance sheet approach, the fair value measurement and the revenue-expense approach (Hints, 2007). The main innovations are associated with the use of the balance sheet approach and the fair value measurement because, traditionally, public accounting systems are mainly focused on the revenue-expense approach and on historical cost valuation (Oulasvirta, 2014).