3,382 research outputs found
Aplicaciones de las nuevas tecnologías en la educación científica: análisis crítico, perspectivas y propuestas
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
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
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
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
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
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
In mould laser welding for high precision polymer based optical components
Assembling a complete subsystem as a rear lamp, it is necessary several different machines and tasks, for
producing the final product. The technology presented in this paper has de capability to reduce the number of tasks
needed for producing a final subsystem/product. In this case will be necessary only one injection moulding machine
with three injection units. This was achieved by combining several technologies, as in-mould assembling, laser welding
and LEDs.
The challenges began by studying several polymeric materials, for understanding their behavior when they are
welded by a laser beam. This was helpful also for determine the best welding properties. At the same time were
analyzed different conductive polymers. This had the objective to determine their suitability for conducting the electric
current between the different LEDs. The development of the rear lamp was made take in consideration the legislation of
UNECE Vehicle Regulations - 1958 Agreement; Regulation No. 50 -Rev.2 - Position lamps, stop lamps, direction
indicators for motorcycles. The results obtained present good input for producing in the same machine a complete and
functional rear lamp
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
Fiber reinforced thermoplastics compounds for electromagnetic interference shielding applications
Market demands for lightweight and lower cost products drive manufacturers to improve current product portfolios. In the case of electronic devices, the most significant weight originates from the enclosure, traditionally in steel or aluminum, that ensures excellent mechanical and electromagnetic shielding performance. The use of thermoplastics filled with electrically conductive fibers, such as carbon or stainless steel, was investigated as a lightweight and cost-effective alternative to steel sheet for creating electromagnetic interference (EMI) shielding enclosures for electronic devices. This paper presents an EMI shielding analysis workflow for the development of plastic enclosures for an electronic device. The workflow starts by measuring the fiber-reinforced thermoplastic compounds shielding effectiveness (SE) with an experimental method in the 30 MHz–3 GHz frequency band. This analysis helps to filter a vast list of materials with a wide range of shielding performance, 20–100 dB, and allows to obtain empirical data for the second phase of the workflow, computer simulations. Simulations with experimentally adjusted material properties were used to validate the design concept of an enclosure in its early development phase. Results from this study showed that the selected material has better EMI SE performance than a steel sheet venting grid.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by Portugal Incentive System for Research and Technological Development, Project no 36265/2013
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