169 research outputs found
METHODOLOGY FOR AUTOMOTIVE AIR-CONDITIONING CONTROL OPTIMIZATION USING ARTIFICIAL NEURAL NETWORKS
The transient nature of automotive air conditioning systems control is generally achieved through proportionalâintegralâderivative controllers (PIDâs) parameters tunning. Due to the vast database available from decades of automotive manufacturers design and expertise, Artificial Neural Networks (ANN) might be able to identify underlying patterns to predict and properly tune the air-conditioning PID control systems under different thermal requirements. Recently, advances in computational capability have enabled compact embarked systems to rapidly solve complex, multi-variable sets of equations, thus allowing for ANN to promptly calculate tunning parameters and act upon PID controllers. As any new application, technical literature is still scarce. On this research, a coupled PID and 6-layers perceptron ANN system was devised, programmed and used to simulate how an air-conditioning system performance can be optimized through proportionalâintegralâderivative controllers tuning. This proposed setup response was then compared to a conventional heuristic PID tunning method (Ziegler Nichols) to demonstrate how ANNâs can more rapidly stabilize the system output
Measuring the degree of stacking order in graphite by Raman spectroscopy
ArticleCARBON. 46(2):272-275(2008)journal articl
Direct Imaging of Graphene Edges: Atomic Structure and Electronic Scattering
We report an atomically-resolved scanning tunneling microscopy (STM)
investigation of the edges of graphene grains synthesized on Cu foils by
chemical vapor deposition (CVD). Most of the edges are macroscopically parallel
to the zigzag directions of graphene lattice. These edges have microscopic
roughness that is found to also follow zigzag directions at atomic scale,
displaying many ~120 degree turns. A prominent standing wave pattern with
periodicity ~3a/4 (a being the graphene lattice constant) is observed near a
rare-occurring armchair-oriented edge. Observed features of this wave pattern
are consistent with the electronic intervalley backscattering predicted to
occur at armchair edges but not at zigzag edges
A new Raman metric for the characterisation of graphene oxide and its derivatives
Raman spectroscopy is among the primary techniques for the characterisation of graphene materials, as it provides insights into the quality of measured graphenes including their structure and conductivity as well as the presence of dopants. However, our ability to draw conclusions based on such spectra is limited by a lack of understanding regarding the origins of the peaks. Consequently, traditional characterisation techniques, which estimate the quality of the graphene material using the intensity ratio between the D and the G peaks, are unreliable for both GO and rGO. Herein we reanalyse the Raman spectra of graphenes and show that traditional methods rely upon an apparent G peak which is in fact a superposition of the G and Dâ peaks. We use this understanding to develop a new Raman characterisation method for graphenes that considers the Dâ peak by using its overtone the 2Dâ. We demonstrate the superiority and consistency of this method for calculating the oxygen content of graphenes, and use the relationship between the Dâ peak and graphene quality to define three regimes. This has important implications for purification techniques because, once GO is reduced beyond a critical threshold, further reduction offers limited gain in conductivity
On the nature of defects in liquid-phase exfoliated graphene
Liquid-phase exfoliation is one of the most promising routes for large-scale production of multilayer graphene dispersions. These dispersions, which may be used in coatings, composites, or paints, are believed to contain disorder-free graphene multilayers. Here, we address the nature of defects in such samples obtained by liquid-phase exfoliation of graphite powder in N-methyl-2-pyrrolidone. Our Raman spectroscopy data challenge the assumption that these multilayers are free of bulk defects, revealing that defect localization strongly depends on the sonication time. For short ultrasound times, defects are located mainly at the layer edges but they turn out to build up in the bulk for ultrasonic times above 2 h. This knowledge may help to devise better strategies to achieve high-quality graphene dispersions.submittedVersionFil: Bracamonte, MarĂa Victoria. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de FĂsica Enrique Gaviola; Argentina.Fil: Bracamonte, MarĂa Victoria. Universidad Nacional de CĂłrdoba. Facultad de MatemĂĄtica, AstronomĂa y FĂsica; Argentina.Fil: Lacconi, Gabriela InĂ©s. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂmicas. Departamento de FisicoquĂmica; Argentina.Fil: Lacconi, Gabriela InĂ©s. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de Investigaciones en FisicoquĂmica de CĂłrdoba; Argentina.Fil: Urreta, Silvia Elena. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de FĂsica Enrique Gaviola; Argentina.Fil: Urreta, Silvia Elena. Universidad Nacional de CĂłrdoba. Facultad de MatemĂĄtica, AstronomĂa y FĂsica; Argentina.Fil: Foa Torres, Luis Eduardo Francisco. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de FĂsica Enrique Gaviola; Argentina.Fil: Foa Torres, Luis Eduardo Francisco. Universidad Nacional de CĂłrdoba. Facultad de MatemĂĄtica, AstronomĂa y FĂsica; Argentina.FĂsica de los Materiales Condensado
Probing the Nature of Defects in Graphene by Raman Spectroscopy
Raman Spectroscopy is able to probe disorder in graphene through
defect-activated peaks. It is of great interest to link these features to the
nature of disorder. Here we present a detailed analysis of the Raman spectra of
graphene containing different type of defects. We found that the intensity
ratio of the D and D' peak is maximum (~ 13) for sp3-defects, it decreases for
vacancy-like defects (~ 7) and reaches a minimum for boundaries in graphite
(~3.5).Comment: 14 pages, 4 figure
Nitrogen-Functionalized Graphene Nanoflakes (GNFs:N): Tunable Photoluminescence and Electronic Structures
This study investigates the strong photoluminescence (PL) and X-ray excited
optical luminescence observed in nitrogen-functionalized 2D graphene nanoflakes
(GNFs:N), which arise from the significantly enhanced density of states in the
region of {\pi} states and the gap between {\pi} and {\pi}* states. The
increase in the number of the sp2 clusters in the form of pyridine-like N-C,
graphite-N-like, and the C=O bonding and the resonant energy transfer from the
N and O atoms to the sp2 clusters were found to be responsible for the blue
shift and the enhancement of the main PL emission feature. The enhanced PL is
strongly related to the induced changes of the electronic structures and
bonding properties, which were revealed by the X-ray absorption near-edge
structure, X-ray emission spectroscopy, and resonance inelastic X-ray
scattering. The study demonstrates that PL emission can be tailored through
appropriate tuning of the nitrogen and oxygen contents in GNFs and pave the way
for new optoelectronic devices.Comment: 8 pages, 6 figures (including toc figure
Probing Mechanical Properties of Graphene with Raman Spectroscopy
The use of Raman scattering techniques to study the mechanical properties of
graphene films is reviewed here. The determination of Gruneisen parameters of
suspended graphene sheets under uni- and bi-axial strain is discussed and the
values are compared to theoretical predictions. The effects of the
graphene-substrate interaction on strain and to the temperature evolution of
the graphene Raman spectra are discussed. Finally, the relation between
mechanical and thermal properties is presented along with the characterization
of thermal properties of graphene with Raman spectroscopy.Comment: To appear in the Journal of Materials Scienc
The INTERVAL trial to determine whether intervals between blood donations can be safely and acceptably decreased to optimise blood supply: study protocol for a randomised controlled trial
- âŠ