Cohesive soils are found all over the world and can cause significant harm to infrastructure and structures. Many innovative ways to improve the strength of cohesive soils are being explored to ...decrease the negative qualities and make them appropriate for construction applications. The availability of novel materials, in addition to traditional procedures, has boosted the area of soil reinforcement. In the realm of soil stabilisation, the inclusion of nanomaterials is one of the newest creative ideas. In geotechnical engineering, nanotechnology could be viewed as dual methods: the composition of the soil can be found at the nanoscale, and soil modification can be accomplished at the atomic and molecular levels. The goal of this research is to see if it is possible to stabilise cohesive soil using two distinct nanomaterials and to look at the changes in geotechnical parameters. Nanocrystalline magnesium oxide and nano zinc oxide is included in the soil with (0.25, 0.5, 0.75 and 1) w/% and trials were executed to evaluate the optimal percent and strength properties of the mixtures.
U radu je opisan postupak projektovanja i izrade kristalnih filtara na bazi kristala kvarca, koji rade na učestanosti od 70 MHz, a koji imaju kontrolisanu faznu karakteristiku. Novi tip kristalnog ...filtra propusnika učestanosti sa centralnom frekvencijom 70MHz projektovan je prema zahtevima korisnika opisanim u listi tehničkih podataka. Ovakvi filtra imaju razne namene u vojnim i civilnim telekomunikacijama.
Carbon nanotubes are rolled up graphene sheets with a quasi-one-dimensional structure of nanometer-scale diameter. In these last twenty years, carbon nanotubes have attracted much attention from ...physicists, chemists, material scientists, and electronic device engineers, because of their excellent structural, electronic, optical, chemical and mechanical properties. More recently, demand for innovative industrial applications of carbon nanotubes is increasing. This book covers recent research topics regarding syntheses techniques of carbon nanotubes and nanotube-based composites, and their applications. The chapters in this book will be helpful to many students, engineers and researchers working in the field of carbon nanotubes.
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We present structural and electronic properties of the cubic structure for different concentrations x of
ternary alloy $B_x Ga_{1-x}N$. The computational method is based on the full-potential ...linearised augmented
plane wave method (FP-LAPW). The exchange and correlation energy is described in the local density
approximation (LDA) and generalized gradient approximation (GGA). We have investigated the effect
of composition on the ground state properties, lattice parameters, bulk modulus, pressure derivative and
band gap of the zinc blend BN and GaN. The results obtained are in a good agreement with experimental
and theoretical values concerning the variation of the gaps and crossover direct, indirect band gap and
the bowing parameter. A reasonable agreement is found from the comparison of our results with other theoretical calculations.
Provider: - Institution: - Data provided by Europeana Collections- In this thesis we investigate electromagnetic composite materials in order to
realize media with the electromagnetic properties not ...achievable in the
nature. The investigated composites are one dimensional and two dimensional
photonic and plasmonic crystals. One dimensional structures consist of
appropriately shaped slabs, whereas two dimensional structures consist of
rods in air or cylindrical holes in a dielectric host. Beside the structures
with the periodic arrangement of the unit cells, we consider graded
structures obtained by a spatial variation of either cells’ geometry or
dielectric permittivity. Photonic crystals are all dielectric structures
whereas the plasmonic crystals are combination of dielectric and plasmonic
materials, metals or semiconductors. Special class of the composite
structures are the planar plasmonic crystals which consist of parallel
ribbons made from plasmonic material on a dielectric substrate. All
composites are considered in the metamaterial regime where unit cell size of
the composites are not negligible in comparison to light wavelength, but the
effective parameters can be still well defined. Homogenization of both one
and two dimensional structures are done within the framework of Maxwell
Garnett theory. Planar plasmonic crystals are not described by effective
parameters, but they are considered as arrays of the same and subwavelength
resonators with well defined plasmonic resonances so the resonant behaviour
of the plasmonic crystals is the collective response of all resonators.
Special attention is devoted to the choice of appropriate materials in the
composites. The structures aimed for guiding of electromagnetic field should
have as low as possible losses so the structures built form dielectrics only
are the most preferably in this case. The plasmonic materials such as metals
or semiconductors have to be used in the following cases: in the realization
of extreme anisotropy in the dielectric permittivity and in the realization
of resonant structures. The first method investigated for guiding of
electromagnetic field is transformation optics. In this method, straight
field trajectories in free space are appropriately transformed into the
desired field trajectories. Maxwell equations are invariant under the applied
coordinate transformations while the material parameters are scaled
accordingly. The obtained material parameters are described with anisotropic
and spatially inhomogeneous dielectric permittivity and magnetic permeability
in a general case. Here we show the procedures for simplifying this material
parameters by considering the concept of reduced parameters by retaining the
same dispersion relation or the concept of the transformations with unit
Jacobian matrix. As a result of the applied procedures, we show that it is
possible to realize transformation optical devices by anisotropic and
spatially inhomogeneous dielectric permittivity. The anisotropy can be then
realized by layered slabs, while the inhomogeneity can be realized by proper
gradation of slab thicknesses and permittivities. Due to large anisotropy in
dielectric permittivity, unit cells have to contain at least one plasmonic
slab. The utilization of the plasmonic materials introduces losses and makes
the bandwidth narrow. For this reason, we consider the methods of
transformation optics with conformal transformation and gradient refractive
index optics where guiding of electromagnetic field is realized by
inhomogeneous and isotropic refractive index. These structures can be then
realized by two dimensional graded photonic crystals where gradation of
refractive index is implemented by gradation of rod or hole radii. Due to
utilization of dielectrics only, these structures are lossless and work in a
broad bandwidth. In order to dynamically control trajectories of
electromagnetic fields, we consider two dimensional graded plasmonic crystals
with semiconductor rods. Permittivity of semiconductor rods can be tuned by
modulating their charge carrier concentration. In this way it is possible to
tune effective graded permittivity of whole graded plasmonic crystals. This
enables a design of structures with dynamical beam steering and focusing.
Beside guiding of electromagnetic fields, we investigate electromagnetic
composite structures which control the field in the frequency domain. They
are based on plasmonic photonic band gaps in two dimensional plasmonic
crystals. The plasmonic gaps arise due to localized surface plasmon
resonances in the rods when electric field is normal to them. Broad
applications of these plasmonic crystals are supported by current development
of new plasmonic materials whose plasma frequency can be well controlled by
fabrication processes. In this way, it is possible to design plasmonic
crystals with the plasmonic photonic band gaps from visible to near-infrared
and even terahertz frequency range. The reason why we investigate the
plasmonic photonic band gaps is twofold: they are both very robust to
disorder and they are very sensitive to the modulation of charge carrier
concentration in the semiconductor rods. The first property candidates
plasmonic crystals as robust photonic band gap media fabricated by the
bottom-up technologies which always result in disordered structures. The
second property of the plasmonic crystals enables design of very sensitive
terahertz modulators and switches. The importance of the new plasmonic
materials is shown in the example of planar one dimensional plasmonic
crystals made from graphene ribbons. Graphene supports surface plasmon
polaritons in wide range of infrared part of the spectrum where utilization
of noble metals is not possible for this purpose. Patterning of graphene into
ribbons enables efficient coupling of incident electromagnetic field into
localized surface plasmon polaritons. We investigate the possibility to
utilize these resonances for plasmonic sensors of dielectric environment at
infrared frequencies. It is shown that graphene based sensors enable sensing
of deep-subwavelength dielectric films as well as sensing of vibration modes
in thin molecular films. As a possible method for graphene patterning, we use
tapping mode atomic force microscopy, that is, dynamic plowing lithography of
exfoliated graphene on silicondioxide substrates. The shape of the graphene
sheet is determined by the movement of the vibrating probe of an atomic force
microscope. There are two possibilities for lithography depending on the
applied force. At moderate forces, the tip only deforms graphene and
generates local strain in the order of 0.1%. For sufficiently large forces,
the tip can hook graphene and then pull it, thus cutting the graphene along
the direction of the tip motion. Electrical characterization by electric
force microscopy allows to distinguish between the truly separated islands
from those still connected to the surrounding graphene.- U ovoj tezi su istraženi elektromagnetski kompozitni materijali u cilju
realizacije sredina sa elektromagnetskim osobinama koje ne postoje u
prirodnim materijalima. Istraživani kompoziti su jednodimenzionalni i
dvodimenzionalni fotonski i plazmonski kristali. Jednodimenzionalne strukture
se sastoje od slojeva odgovarajućeg oblika, dok se dvodimenzionalne strukture
sastoje od štapića u vazduhu ili cilindričnih rupa u dielektriku. Pored
struktura sa periodičnim ponavljanjem jediničnih ćelija, razmatraju se i
gradirane strukture dobijene prostornom promenom geometrije ili dielektrične
permitivnosti jediničnih ćelija. Fotonski kristali se sastoje isključivo od
dielektrika, dok su plazmonski kristali kombinacija dielektričnih i
plazmonskih materijala, metala ili poluprovodnika. Posebna klasa razmotrenih
kompozitnih struktura su planarni plazmonski kristali koji se sastoje od
paralelnih traka od plazmonskih materijala na dielektričnom substratu. Sve
kompozitne strukture se razmatraju u režimu metamaterijala gde veličina
jedinične ćelije nije zanemarljiva u odnosu na talasnu dužinu svetlosti, ali
se efektivni parametri ipak mogu definisati. I jednodimenzionalne i
dvodimenzionalne strukture su homogenizovane pomoću Maksvel Garnetove
teorije. Planarni plazmonski kristali nisu opisani efektivnim parametrima,
nego se razmatraju kao nizovi istih i podtalasnih rezonatora sa definisanim
plazmonskim rezonancijama tako da rezonantne karakteristike plazmonskih
kristala predstavljaju kolektivni odziv svih rezonatora. Posebna pažnja je
posvećena izboru odgovarajućih materijala u kompozitima. Strukture namenjene
vođenju elektromagnetskog polja treba da imaju što manje gubitke tako da u
ovom slučaju strukture treba da budu isključivo dielektrične. Plazmonski
materijali kao što su metali i poluprovodnici se moraju koristiti u sledećim
slučajevima: u realizaciji visoke anizotropije dielektrične permitivnosti i u
realizaciji rezonantnih struktura. Prvi metod koji je istraživan za vođenje
elektromagnetskog polja je transformaciona optika. U ovom metodu, prave
linije polja u slobodnom prostoru se na odgovarajući način transformišu u
linije polja sa željenim oblikom. Maksvelove jednačine su invarijantne
prilikom koordinatnih transformacija dok se materijalni parametri menjaju u
skladu sa primenjenom transformacijom. Dobijeni materijalni parametri su
opisani anizotropnom i prostorno nehomogenom dielektričnom permitivno šću i
magnetskom peremabilnošću u opštem slučaju. Ovde je data procedura kojom se
nalaze jednostavniji materijalni parametri pomoću koncepta redukovanih
parametara pri čemu se zadržava ista disperzija ili pomoću koncepta
transformacija sa jediničnim Jakobijanom. Kao rezultat primenjenih procedura,
pokazuje se da je moguće realizovati uređaje na bazi transformacione optike
pomoću anizotropne i prostorno nehomogene dielektrične permitivnosti.
Anizotropija je onda realizovana slojevima ploča, dok se nehomogenost može
realizovati odgovarajućom gradacijom debljine
Many of today’s technologies and research techniques depend on process and methods in high and ultra-high vacuum chambers. High temperature vacuum chambers require innovative concept and use of ...unusual materials in design to achieve quality performance. In order to obtain quality performance, the temperature and gas delivery on the vacuum chamber surface must be uniformly distributed. In this work, a new funnel for high temperature vacuum chamber was successfully designed and tested using computer-based simulation techniques. The funnel was made of quartz crystal (Grade 2) due to ability to absorb temperature, properties of low gas permeability and low temperature coefficient. In order to mitigate O-rings from high temperature failure and to reduce non-uniformity effect during temperature delivery, a new quartz funnel was developed. The simulation and experimental results show that uniformity distributions in temperature of vacuum chamber surface were obtained with new funnel design.Özet: Günümüz teknolojilerinin ve araştırma tekniklerinin çoğu yüksek ve ultra yüksek vakum odalarındaki proses ve metotlara bağlıdır. Yüksek sıcaklık vakum odaları, yenilikçi kavram ve kaliteli performans elde edilen tasarımda alışılagelmedik malzemelerin kullanımını gerektirir. Kaliteli performans elde etmek için vakum odası yüzeyine sıcaklık ve gaz iletimi eşit dağılmalıdır. Bu çalışmada, bilgisayar bazlı simülasyon teknikleri kullanılarak yüksek sıcaklık vakum odası için yeni bir huni tasarımı başarılı bir şekilde tasarlanmış ve test edilmiştir. Huni, sıcaklık emme yeteneği, düşük gaz geçirgenliği ve düşük sıcaklık katsayısı özellikleri sebebi ile kuvars kristalinden yapılmıştır. Sıcaklık iletimi esnasında eşit olmayan dağılımın etkisini azaltmak ve yüksek sıcaklık düşüşlerini düşürmek için yeni bir kuvars huni geliştirilmiştir. Simülasyon ve deney sonuçları gösterdi ki, vakum odası yüzeyinin sıcaklığındaki eşit dağılımlar yeni huni tasarımı ile elde edilmiştir.
The two-body pairwise E.G.E.P. (Extended Generalized Exponantial Potential) type Morse potential and volume dependent energy are assumed to represent the total energy of the Ba crystal. The ...parametrized potential is used to calculate the second- and third-order elastic constants $C_{ij}$ and $C_{ijk}$, pressure derivatives of bulk moduli and Grüneisen parameter $\gamma$ . The phonon frequencies are also computed and plotted. The obtained results are compared with available experimental data and, in general, the agreement is good.
