Formation of Atomic Carbon Chains from Graphene Nanoribbons

The formation of one-dimensional carbon chains from graphene nanoribbons is investigated using it ab initio molecular dynamics. We show under what conditions it is possible to obtain a linear atomic chain via pulling of the graphene nanoribbons. The presence of dimers composed of two-coordinated carbon atoms at the edge of the ribbons is necessary for the formation of the linear chains, otherwise there is simply the full rupture of the structure. The presence of Stone-Wales defects close to these dimers may lead to the formation of longer chains. The local atomic configuration of the suspended atoms indicates the formation of single and triple bonds, which is a characteristic of polyynes.Comment: 4 pages, 5 figure

Combination of laser welding with in-mould assembling into a single process

The search of a process capable of produce and assemble complex subsystems in a short period is the goal of any company. In the market it is possible to found several solutions. They go from simple glue to the complexes systems that use moulds, robot and other. These systems are part of a complex assembling line. In these lines are several different processes as welding, plastic and assembling process. This complex structure is costly, and in countries where the labour cost is high. To maintain the cost the companies are obliged to go overseas. The process presented had the objective of reducing the complexity of an assembling line. The reduction of the complexity is achieved through the combination of the in-mould assembly and the laser welding. The in-mould assembly is used to produce in the same mould several components. Laser welding is used to join different polymers. To study the viability of the process I was chosen a case study, in this case, a rear lamp. Firstly, it was modified to this new process, and then each component was studied individually. Finally, all the processes were combined and it was concluded that this process has viability and to make it possible producing a complex subsystem in one process

Microinjection of polipropylene with nanoclays

Polypropylene (PP)/montmorillonite (MMT) nanocomposites micro samples was produced by micro injection molding at concentrations 2, 6 and 10% of Nanomax. The dispersion of the nanoclay particles in polypropylene was characterized using optical microscopy in polarized light, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) and the mechanical characterisation was performed using the tensile test. The results of x-ray diffraction indicated the formation of nanocomposites with partially exfoliated or intercalated structures, depending on the concentration of clay, with a maximum basal spacing of 6.217 nm. The micrographs obtained by scanning electron microscopy of fractured nanocomposite showed good dispersion of clay in polymer matrix without the presence of clusters. The tensile strength of PP/MMT is not much improved compared with pure PP but deformation increased significantly

In mold laser welding for high precision polymer based optical components

“Proceedings of PPS-29 : The 29th International Conference of the Polymer Processing Society - Conference Papers. ISBN 978-0-7354-1227-9”To Assemble a complete subsystem as a rear lamp, is necessary to have different machines and to perform several tasks. This necessity obliges the companies to have large structures to support all the assembling process. These huge structures are very costly and have as a consequence the reduction of the competitiveness of the companies. The process presented in this document has the intention of reducing the number of tasks needed to produce the final subsystem/product. To achieve this goal were combined several technologies, as in-mould assembling, laser welding and LEDs (light-emitting diode). One of the advantages of this process was the utilization of only one injection molding machine with three injection units to do all the assembling process. To achieve the main objective, firstly, the rear lamp was designed according to with the legislation of UNECE Vehicle Regulations - 1958 Agreements; Regulation No. 50 -Rev.2 - Position lamps, stop lamps, direction indicators for motorcycles. Posterior several polymeric materials were studied at different levels. Initial were studied several concentrations of carbon nanotubes mixed with PC (polycarbonate). This had the objective of determine, if these materials are suitable to conduct the necessary electric current to turn on the different LEDs. One of the main advantages of this process is the use of the laser transmission welded process. Since, with this welding technology is possible reduce the complexity of the final part. To understand the potentialities of this technology a combination of two materials was studied. The studied showed that all materials presented a high transparency to the laser beam. In terms of weld process, the study showed that the best welding conditions are the lowest velocity, diameter and power. With these studies was possible conclude that this new process is suitable to be implemented at the industrial level

Thermoelectrical regulation of microinjection moulds

Microinjection is one of the major replication techniques for producing low cost micro parts. The small scale of the microinjection processes presents different challenges from those usually encountered in conventional injection moulding. One particular aspect, very important for part quality, is mould temperature control. In conventional injection moulding, the temperature control system is set to a fixed value during the injection cycle. In microinjection moulding such behaviour is not acceptable, which as lead to the development of “active” control temperature of the mould named “variotherm” systems. In the present paper a study will be presented for the implementation of thermo electric elements in dynamic temperature control of microinjection moulds and its impact on the process cycle time and part quality

Effect of the Injection moulding processing conditions on biopolymers final properties

This research work intended to study the effect of the main injection moulding parameters in the final properties of biopolymers mouldings. An experimental procedure was carried out in which four biopolymers containing different composition percentages of poly-lactic acid (PLA) and plasticized starch (PLS) were compared with polypropylene (PP). For each material the effect of the processing conditions (mould temperature, injection temperature and holding pressure) on the final properties was discussed and the possibility of using biopolymers as a substitute of PP in household utility products was evaluated

Evaluation of coefficient of friction in similar conditions to ejection of molding parts

The injection molding is the technique most used for processing polymers. Nowadays, due to economic demands the ejection of the parts occur as soon as possible to lead to a short cycle times. The ejection stage is the most critical phase during the injection molding processing. During this stage, especially in deep core molding, it is possible the development high friction forces making difficult the ejection of the moldings without marks or other defects. The aim of this work is to assess the coefficient of friction between the part and the mould walls in conditions similar that occurs during the ejection in the injection molding process. The assessment of the coefficient of friction was carried out with the help of one apparatus that possibility this type of measurement. This equipment provides that measure under controlled conditions as test temperature, replication temperature, material of the mould, and superficial roughness. The obtained results with several polymeric materials (semicrystalline and amorphous) show that the tribological conditions have great influence on the coefficient of friction in static conditions

Emphasis on Mathematical Modeling: The Problems of Contour Values in Calculating the Deflection of a Beam

Mathematical Modeling has played a fundamental role in the process of teaching and learning mathematics at the various levels of education. The great challenge of today\u27s education is to create means to minimize the distance between the relations of mathematical theory and practical models of everyday life. This work aimed to treat the study of Ordinary Differential Equations through a very usual model of civil construction. Often, students of Mathematics Degree develop skills to understand the abstractions of the vast theory associated with the areas of mathematics, but without being able to exemplify and / or correlate with everyday models

Barrierless procedure for substitutionally doping graphene sheets with boron atoms: ab initio calculations

Using ab initio methods, we propose a simple and effective way to substitutionally dope graphene sheets with Boron. The method consists of selectively exposing each side of the graphene sheet to different elements. We first expose one side of the membrane to Boron, while the other side is exposed to Nitrogen. Proceeding this way, the B atoms will be spontaneously incorporated into the graphene membrane, without any activation barrier. In a second step, the system should be exposed to a H-rich environment, that will remove the CN radical from the layer and form HCN, leading to a perfect substitutional doping.Comment: Accepted Physical Review