78 research outputs found
Simulation of hydrogenated graphene Field-Effect Transistors through a multiscale approach
In this work, we present a performance analysis of Field Effect Transistors
based on recently fabricated 100% hydrogenated graphene (the so-called
graphane) and theoretically predicted semi-hydrogenated graphene (i.e.
graphone). The approach is based on accurate calculations of the energy bands
by means of GW approximation, subsequently fitted with a three-nearest neighbor
(3NN) sp3 tight-binding Hamiltonian, and finally used to compute ballistic
transport in transistors based on functionalized graphene. Due to the large
energy gap, the proposed devices have many of the advantages provided by
one-dimensional graphene nanoribbon FETs, such as large Ion and Ion/Ioff
ratios, reduced band-to-band tunneling, without the corresponding disadvantages
in terms of prohibitive lithography and patterning requirements for circuit
integration
Carbon release by selective alloying of transition metal carbides
We have performed first principles density functional theory calculations on
TiC alloyed on the Ti sublattice with 3d transition metals ranging from Sc to
Zn. The theory is accompanied with experimental investigations, both as regards
materials synthesis as well as characterization. Our results show that by
dissolving a metal with a weak ability to form carbides, the stability of the
alloy is lowered and a driving force for the release of carbon from the carbide
is created. During thin film growth of a metal carbide this effect will favor
the formation of a nanocomposite with carbide grains in a carbon matrix. The
choice of alloying elements as well as their concentrations will affect the
relative amount of carbon in the carbide and in the carbon matrix. This can be
used to design the structure of nanocomposites and their physical and chemical
properties. One example of applications is as low-friction coatings. Of the
materials studied, we suggest the late 3d transition metals as the most
promising elements for this phenomenon, at least when alloying with TiC.Comment: 9 pages, 6 figure
Evolving properties of two dimensional materials, from graphene to graphite
We have studied theoretically, using density functional theory, several
materials properties when going from one C layer in graphene to two and three g
raphene layers and on to graphite. The properties we have focused on are the
elastic constants, electronic structure (energy bands and density of state s),
and the dielectric properties. For any of the properties we have investigated
the modification due to an increase in the number of graphene layers is within
a few percent. Our results are in agreement with the analysis presented
recently by Kopelevich and Esquinazi (unpublished)
Challenges and opportunities in linking carbon sequestration, livelihoods and ecosystem service provision in drylands
Database-driven High-Throughput Calculations and Machine Learning Models for Materials Design
This paper reviews past and ongoing efforts in using high-throughput ab-inito
calculations in combination with machine learning models for materials design.
The primary focus is on bulk materials, i.e., materials with fixed, ordered,
crystal structures, although the methods naturally extend into more complicated
configurations. Efficient and robust computational methods, computational
power, and reliable methods for automated database-driven high-throughput
computation are combined to produce high-quality data sets. This data can be
used to train machine learning models for predicting the stability of bulk
materials and their properties. The underlying computational methods and the
tools for automated calculations are discussed in some detail. Various machine
learning models and, in particular, descriptors for general use in materials
design are also covered.Comment: 19 pages, 2 figure
GreenPilot, lotsbÄt med minimal miljöpÄverkan
The GreenPilot project was carried out to demonstrate the emissions reductions and environmental performance improvements that could be achieved by converting a small vessel to run on methanol fuel. Reducing emissions is a priority for all vessel sizes, as emissions regulations are becoming stricter and concern about greenhouse gases and global warming continues to grow. Within Sweden, the government has announced its ambition to convert all state-owned vessels to fossil-free operation and is investigating 2030 and 2045 as possible deadlines. Methanol produced from renewable feedstock is a possible solution for some of the vessels. By physically converting a Swedish pilot boat to run on methanol, the project demonstrated he feasibility of methanol as a fuel solution for small vessels. Work included converting and testing three different engines to run on methanol, two of which were installed and operated on the converted pilot boat. Emissions measurements showed good reductions as compared to conventional fuel oil. Fossil-free methanol produced from pulp mill black liquor in a Swedish pilot plant was used in some of the laboratory and on board tests. The project also investigated other solutions for reducing environmental impacts of the pilot boats, including the use of solar cells, batteries, and fuel cells.GreenPilot-projektet genomfördes för att demonstrera utslÀppsminskningar ochmiljöprestanda förbÀttringar som kan uppnÄs genom att konvertera en litenkÀrl att köra pÄ metanolbrÀnsle. Att minska utslÀppen Àr en prioritet för alla fartygsstorlekar, somUtslÀppsreglerna blir hÄrdare och oroa sig för vÀxthusgaser och globalauppvÀrmning fortsÀtter att vÀxa. Inom Sverige har regeringen meddelat sin ambition attkonvertera alla statligt Àgda fartyg till fossilfri drift och undersöker 2030 och 2045 sommöjliga tidsfrister. Metanol framstÀlld av förnybart rÄmaterial Àr en möjlig lösning förnÄgra av fartygen.Genom att fysiskt konvertera en svensk pilotbÄt för att köra pÄ metanol visade projektethan genomförbarhet av metanol som en brÀnsle lösning för smÄ fartyg. Arbetet inkluderade konvertering ochtesta tre olika motorer för att köra pÄ metanol, varav tvÄ installerades och drivsGreenPilot, lotsbÄt med minimal miljöpÄverka
A multi-scale approach for performance assessment of hydrogenated graphene Field-Effect Transistors
An open-source optimization tool for solar home systems: A case study in Namibia
Solar home systems (SHSs) represent a viable technical solution for providing electricity to households and improving standard of living conditions in areas not reached by the national grid or local grids. For this reason, several rural electrification programmes in developing countries, including Namibia, have been relying on SHSs to electrify rural off-grid communities. However, the limited technical know-how of service providers, often resulting in over- or under-sized SHSs, is an issue that has to be solved to avoid dissatisfaction of SHSsâ users. The solution presented here is to develop an open-source software that service providers can use to optimally design SHSs components based on the specific electricity requirements of the end-user.
The aim of this study is to develop and validate an optimization model written in MS Excel-VBA which calculates the optimal SHSs components capacities guaranteeing the minimum costs and the maximum system reliability. The results obtained with the developed tool showed good agreement with a commercial software and a computational code used in research activities. When applying the developed optimization tool to existing systems, the results identified that several components were incorrectly sized. The tool has thus the potentials of improving future SHSs installations, contributing to increasing satisfaction of end-users
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