192 research outputs found
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The polycyclic aromatic hydrocarbon concentrations in soils in the Region of Valasske Mezirici, the Czech Republic
The polycyclic aromatic hydrocarbon (PAH) contamination of urban, agricultural and forest soil samples was investigated from samples obtained in the surroundings of Valasske Mezirici. Valasske Mezirici is a town located in the north-east mountainous part of the Czech Republic, where a coal tar refinery is situated. 16 PAHs listed in the US EPA were investigated. Organic oxidizable carbon was also observed in the forest soils. The PAH concentrations ranged from 0.86-10.84 (with one anomalous value of 35.14) and 7.66-79.39 mg/kg dm in the urban/agricultural and forest soils, respectively. While the PAH levels in the urban/agricultural soils are within the range typically found in industrialized areas, the forest soils showed elevated PAH concentrations compared to other forest soils in Western and Northern Europe. The PAH concentrations and their molecular distribution ratios were studied as functions of the sample location and the meteorological history. The soils from localities at higher altitudes above sea level have the highest PAH concentrations, and the PAH concentrations decrease with increasing distance from the town
The polycyclic aromatic hydrocarbon concentrations in soils in the Region of Valasske Mezirici, the Czech Republic
The polycyclic aromatic hydrocarbon (PAH) contamination of urban, agricultural and forest soil samples was investigated from samples obtained in the surroundings of Valasske Mezirici. Valasske Mezirici is a town located in the north-east mountainous part of the Czech Republic, where a coal tar refinery is situated. 16 PAHs listed in the US EPA were investigated. Organic oxidizable carbon was also observed in the forest soils. The PAH concentrations ranged from 0.86-10.84 (with one anomalous value of 35.14) and 7.66-79.39 mg/kg dm in the urban/agricultural and forest soils, respectively. While the PAH levels in the urban/agricultural soils are within the range typically found in industrialized areas, the forest soils showed elevated PAH concentrations compared to other forest soils in Western and Northern Europe. The PAH concentrations and their molecular distribution ratios were studied as functions of the sample location and the meteorological history. The soils from localities at higher altitudes above sea level have the highest PAH concentrations, and the PAH concentrations decrease with increasing distance from the town
In situ observations of freestanding single-atom-thick gold nanoribbons suspended in graphene
Bulk gold's attributes of relative chemical inertness, rarity, relatively low melting point and its beautiful sheen make it a prized material for humans. Recordings suggest it was the first metal employed by humans dating as far back to the late Paleolithic period approximate to 40 000 BC. However, at the nanoscale gold is expected to present new and exciting properties, not least in catalysis. Moreover, recent studies suggest a new family of single-atom-thick two-dimensional (2D) metals exist. This work shows single-atom-thick freestanding gold membranes and nanoribbons can form as suspended structures in graphene pores. Electron irradiation is shown to lead to changes to the graphene pores which lead to dynamic changes of the gold membranes which transition to a nanoribbon. The freestanding single-atom-thick 2D gold structures are relatively stable to electron irradiation for extended periods. The work should advance the development of 2D gold monolayers significantly.Web of Scienceart. no. 200043
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High power Q-switched thulium doped fibre laser using carbon nanotube polymer composite saturable absorber
We have proposed and demonstrated a Q-switched Thulium doped fibre laser (TDFL) with a ‘Yin-Yang’ all-fibre cavity scheme based on a combination of nonlinear optical loop mirror (NOLM) and nonlinear amplified loop mirror (NALM). Unidirectional lasing operation has been achieved without any intracavity isolator. By using a carbon nanotube polymer composite based saturable absorber (SA), we demonstrated the laser output power of ~197 mW and pulse energy of 1.7 μJ. To the best of our knowledge, this is the highest output power from a nanotube polymer composite SA based Q-switched Thulium doped fibre laser
The catalytic potential of high-k dielectrics for graphene formation
The growth of single and multilayer graphene nano-flakes on MgO and ZrO2 at
low temperatures is shown through transmission electron microscopy. The
graphene nano-flakes are ubiquitously anchored at step edges on MgO (100)
surfaces. Density functional theory investigations on MgO (100) indicate C2H2
decomposition and carbon adsorption at step-edges. Hence, both the experimental
and theoretical data highlight the importance of step sites for graphene growth
on MgO
Growth of all-carbon horizontally aligned single-walled carbon nanotubes nucleated from fullerene-based structures
All-carbon single-walled carbon nanotubes (SWCNTs) were successfully synthesized, nucleated using a fullerene derivative. A systematic investigation into the initial preparation of C60 fullerenes as growth nucleators for the SWCNTs was conducted. Enhancement in the yield of the produced SWCNT has been achieved with exploring different dispersing media for the fullerenes, the period, and environment of the initial thermal treatment of the fullerenes in addition to the use of different fullerene-based structures. The systematic studies significantly advance our understanding of the growth of the all-carbon catalyst-free single-walled carbon nanotubes. Field-effect transistors were fabricated using the catalyst-free SWCNT and then electrically characterized, showing current capacity as high as the well-studied catalyst-assisted nanotubes
Graphene: Piecing it together
Graphene has a multitude of striking properties that make it an exceedingly
attractive material for various applications, many of which will emerge over
the next decade. However, one of the most promising applications lie in
exploiting its peculiar electronic properties which are governed by its
electrons obeying a linear dispersion relation. This leads to the observation
of half integer quantum hall effect and the absence of localization. The latter
is attractive for graphene-based field effect transistors. However, if graphene
is to be the material for future electronics, then significant hurdles need to
be surmounted, namely, it needs to be mass produced in an economically viable
manner and be of high crystalline quality with no or virtually no defects or
grains boundaries. Moreover, it will need to be processable with atomic
precision. Hence, the future of graphene as a material for electronic based
devices will depend heavily on our ability to piece graphene together as a
single crystal and define its edges with atomic precision. In this progress
report, the properties of graphene that make it so attractive as a material for
electronics is introduced to the reader. The focus then centers on current
synthesis strategies for graphene and their weaknesses in terms of electronics
applications are highlighted.Comment: Advanced Materials (2011
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Microscopic insight into the bilateral formation of carbon spirals from a symmetric iron core
Mirrored carbon-spirals have been produced from pressured ferrocene via the bilateral extrusion of the spiral pairs from an iron core. A parametric plot of the surface geometry displays the fractal growth of the conical helix made with the logarithmic spiral. Electron microscopy studies show the core is a crystalline cementite which grows and transforms its shape from spherical to biconical as it extrudes two spiralling carbon arms. In a cross section along the arms we observe graphitic flakes arranged in a herringbone structure, normal to which defects propagate. Local-wave-pattern analysis reveals nanoscale defect patterns of two-fold symmetry around the core. The data suggest that the bilateral growth originates from a globular cementite crystal with molten surfaces and the nano-defects shape emerging hexagonal carbon into a fractal structure. Understanding and knowledge obtained provide a basis for the controlled production of advanced carbon materials with designed geometries
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