Ejection force of tubular injection moldings. Part II: A prediction model

The integrated knowledge of the injection molding process and the material changes induced by processing is essential to guarantee the quality of technical parts. In the case of parts with deep cavities, quite often the ejection phase of the molding cycle is critical. Thus, in the mold design stage, the aspects associated with the ejection system will require special consideration. In particular, the prediction of the ejection force will contribute to optimizing the mold design and to guarantee the integrity of the moldings. In this work, a simulation algorithm based on a thermomechanical model is described and their predictions are compared with experimental data obtained from a fully‐instrumented mold (pressure, temperature, and force). Three common thermoplastics polymers were used for the tubular moldings: a semicrystalline polypropylene and two amorphous thermoplastics: polystyrene and polycarbonate. The thermomechanical model is based on the assumption of the polymer behavior changing from purely viscous to purely elastic below a transition point. This point corresponds to solidification determined by temperature in the case of amorphous materials and by critical crystallinity for semicrystalline polymers. The model results for the ejection force closely agree with the experimental data for the three materials used. POLYM. ENG. SCI. 45:325–332, 2005. © 2005 Society of Plastics Engineers.     

Adapting the Olgyay bioclimatic chart to assess local thermal comfort levels in urban regions

Clean Technologies and Environmental Policy - Providing comfortable thermal conditions for users of open spaces is vitally important for improving the quality of urban life. Thermal comfort can be...     

Construction and qualitative assessment of a bibliographic portfolio using the methodology Methodi Ordinatio

Methodi Ordinatio is a methodology used to accomplish systematic literature reviews, to build bibliographical portfolios, and to map the state of the art of a research theme. It is composed of nine phases. The 7th phase, named InOrdinatio, applies an equation that orders the papers according to its scientific relevance. The equation applies the alpha (α) element, which can vary from 0 to 10 depending on the research need of currentness and according to the researcher’s perception for its variation. Therefore, the aim of this paper is to test and analyse the variations of the alpha (α) values in the equation InOrdinatio and its influence in the qualification of the items that composes a portfolio. In order to reach this purpose, a practical application was performed and a bibliographic portfolio on the theme Horizontal Business Networks and Trust was built. Using the data from the bibliographic portfolio, the alpha values from 0 to 10 were applied and their influence on the final qualification of the articles was analysed. As a complementary objective, the areas where the methodology was successfully applied until now are also identified. The results show that the methodology is coherent, reproducible and useful to sort the most relevant articles in accordance with what is internationally recognized as valid scientific criteria: the impact factor, year of publication, and number of citations.     

Meningoencephalitis due to Rickettsia conorii. Etiopathological, clinical and diagnostic aspects

Boutonneuse fever (BF) is usually considered to be a benign rickettsiosis. However, severe presentations, resembling Rocky Mountain spotted fever, have been reported. There are few neurological complications, except in serious forms of the disease. We present a case of meningoencephalitis in a male adult suffering from BF, and we review the clinical, etiopathogenic and diagnostic aspects among the cases previously reported. We conclude that BF encephalitis would have the following characteristics: a) they mostly affect elderly males; b) they cause altered consciousness level, headaches and low rate of meningeal signs; c) absence of "tache noir"; d) cerebrospinal fluid with slight pleocytosis and/or increased level of proteins, and normal glucose values; e) computerized tomography without significative changes, and f) high rate of morbidity and mortality. We emphasize that we should consider BF in the differential diagnosis of our environmental encephalitis.     

Networks and firm location

This paper models the decision of vertically linked firms to build either partitioned or connected networks of supply of an intermediate good. In each case, there is a correlation between the locations of upstream and downstream firms. Input specificity is related to both variable costs (transport costs of the input) and fixed costs (learning costs of the use of the input). When both are low, a connected network emerges, whereas, in the opposite case, we find a partitioned pattern. In the boundary region, there are multiple equilibria, either asymmetric (mixed network) or symmetric.     

Ureterostomy in situ: technique for temporary urinary diversion

Ureterostomy in situ is a simple technique for supravesical urinary diversion. Although it was described a few years ago, it has not gained wide acceptance. From our experience and with slight modifications, we believe there is a place for this procedure as a method of temporary urinary diversion.     

A method to estimate statistics of rain depolarization

This paper is concerned with depolarization caused by rain due to nonsphericity of drops and the distribution of their axes orientations. The drops are assumed to be oblate spheroids having canting angles distribution obtained by Saunders. Differential phase shift as well as differential attenuation is important in the calculation of depolarization and the values proposed by Oguchi and Hosoya are utilized. In the first part expression to calculate depolarization amount for a uniform precipitation rate are presented. But communication engineers are usually interested on statistical variations of depolarization amount, so the second part of this paper is concerned with statistical distribution of depolarization. The rain cell proposed by Misme and Fimbel is used to describe the rain model over a path. If the precipitation rate distribution is known in one point of the path, the depolarization distribution is obtained by assuming only one rain cell along the path where, for a long time observation, the precipitation rate distribution for all points is the same.     

Microstructure and electrical properties of perovskite (Pb, La)TiO3 thin film deposited at low temperature by the polymeric precursor method

High-quality (Pb, La)TiO₃ ferroelectric thin films were successfully prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate for the first time by spin coating, using the polymeric precursor method. The X-ray diffraction patterns show that the films are polycrystalline in nature. This method allows for low temperature (500° C) synthesis, a high quality microstructure and superior dielectric properties. The effects on the microstructure and electrical properties were studied by changing the La content. The films annealed at 500°C have a single perovskite phase with only a tetragonal or pseudocubic structure. As the La content is increased, the dielectric constant of PLT thin films increases from 570 up to 1138 at room temperature. The C-V and P-E characteristics of perovskite thin films prepared at a low temperature show normal ferroelectric behavior, representing the ferroelectric switching property. The remanent polarization and coercive field of the films deposited decreased due to the transformation from the ferroelectric to the paraelectric phase with an increased La content.     

Optimal process operation for the production of linear polyethylene resins with tailored molecular weight distribution

An optimization model is presented to determine optimal operating policies for tailoring high density polyethylene in a continuous polymerization process. Shaping the whole molecular weight distribution (MWD) by adopting an appropriate choice of operating conditions is of great interest when designing new polymers or when improving quality. The continuous tubular and stirred tank reactors are modeled in steady state by a set of differential‐algebraic equations with the spatial coordinate as independent variable. A novel formulation of the optimization problem is introduced. It comprises a multi‐stage optimization model with differential‐algebraic equality constraints along the process path and inequality end‐point constraints on product quality. The resulting optimal control problem is solved at high computational efficiency by means of a shooting method. The results show the efficiency of the proposed approach and the benefit of predicting and controlling the complete MWD as well as the interplay between operating conditions and polymer properties. © 2010 American Institute of Chemical Engineers AIChE J, 2011