1,492 research outputs found
Short communication: Study on epilithic diatoms in the Kozluk Creek (Arapgir-Malatya, Turkey)
Being the most important members of phytoplankton and phytobenthos, both of which are the primary producers of surface water resources, algae play a very important role in the biological productivity of waters with their oxygen production through photosynthesis and they synthesize the organic materials. Furthermore, with their high levels of protein, algae are used as human and animal food as well as being used in the production of organic fertilizers and organic vitamins. Another reason for algae currently being among the most researched organisms is their easy and inexpensive productions in culture media. With the recognition of the importance of algae in standing waters and streams, the number of studies conducted on these organisms has rapidly increased. In Turkey, the number of studies on algae in streamsis quite high [(Altuner and Gurbuz (1989), Altuner and Gurbuz (1991) Yıldız (1991) , Yildiz and Ozkiran (1994), Ertan and Morkoyunlu (1998), Sahin (1998), Cetin and Yavuz (2001), Solak et al. (2012), Sivaci and Dere (2007), Mumcu et al. (2009), Pala and Caglar (2008)]
Modelling a cell tower using SFM: automated detection of structural elements from skeleton extraction on a point cloud
The surveying and management of telecommunication towers poses a series of engineering challenges. Not only they must be regularly inspected for the purpose of checking for issues that require maintenance interventions, but they are often sub-let by their owners to communication companies, requiring a survey of the many (several thousand per company) installed appliances to check that they respect the established contracts. This requires a surveying methodology that is fast and possibly automated. Photogrammetric techniques using UAV-mounted cameras seem to offer a solution that is both suitable and economical. Our research team was asked to evaluate whether, from the information acquired by small drones it was possible to obtain geometric information on the structure, with what degree of accuracy and what level of detail. The workflow of this process is naturally articulated in three steps: the acquisition, the construction of the point cloud, and the extraction of geometries. The case study is a tower carrying antennas owned by several operators and placed in the industrial district of Cagliari. The article examines the problems found in modelling such structures using point clouds derived from the Structure-from-Motion technique, in order to obtain a model of nodes and beams suitable for the reconstruction of the structure's geometric elements, and possibly for a finite elements analysis or for populating GIS and BIM, either automatically or with minimal user intervention. In order to achieve this, we have used voxelization and skeleton extraction algorithms to obtain a 3D graph of the structure. The analysis of the results was carried out by varying the parameters relating to the voxel size, which defines the resolution, and the density of the points contained inside each voxel
Spin-orbit coupling and phase-coherence in InAs nanowires
We investigated the magnetotransport of InAs nanowires grown by selective
area metal-organic vapor phase epitaxy. In the temperature range between 0.5
and 30 K reproducible fluctuations in the conductance upon variation of the
magnetic field or the back-gate voltage are observed, which are attributed to
electron interference effects in small disordered conductors. From the
correlation field of the magnetoconductance fluctuations the phase-coherence
length l_phi is determined. At the lowest temperatures l_phi is found to be at
least 300 nm, while for temperatures exceeding 2 K a monotonous decrease of
l_phi with temperature is observed. A direct observation of the weak
antilocalization effect indicating the presence of spin-orbit coupling is
masked by the strong magnetoconductance fluctuations. However, by averaging the
magnetoconductance over a range of gate voltages a clear peak in the
magnetoconductance due to the weak antilocalization effect was resolved. By
comparison of the experimental data to simulations based on a recursive
two-dimensional Green's function approach a spin-orbit scattering length of
approximately 70 nm was extracted, indicating the presence of strong spin-orbit
coupling.Comment: 8 pages, 7 figure
Formation of quantum dots in the potential fluctuations of InGaAs heterostructures probed by scanning gate microscopy
The disordered potential landscape in an InGaAs/InAlAs two-dimensional
electron gas patterned into narrow wires is investigated by means of scanning
gate microscopy. It is found that scanning a negatively charged tip above
particular sites of the wires produces conductance oscillations that are
periodic in the tip voltage. These oscillations take the shape of concentric
circles whose number and diameter increase for more negative tip voltages until
full depletion occurs in the probed region. These observations cannot be
explained by charging events in material traps, but are consistent with Coulomb
blockade in quantum dots forming when the potential fluctuations are raised
locally at the Fermi level by the gating action of the tip. This interpretation
is supported by simple electrostatic simulations in the case of a disorder
potential induced by ionized dopants. This work represents a local
investigation of the mechanisms responsible for the disorder-induced
metal-to-insulator transition observed in macroscopic two-dimensional electron
systems at low enough density
Local Density of States in Mesoscopic Samples from Scanning Gate Microscopy
We study the relationship between the local density of states (LDOS) and the
conductance variation in scanning-gate-microscopy experiments on
mesoscopic structures as a charged tip scans above the sample surface. We
present an analytical model showing that in the linear-response regime the
conductance shift is proportional to the Hilbert transform of the
LDOS and hence a generalized Kramers-Kronig relation holds between LDOS and
. We analyze the physical conditions for the validity of this
relationship both for one-dimensional and two-dimensional systems when several
channels contribute to the transport. We focus on realistic Aharonov-Bohm rings
including a random distribution of impurities and analyze the LDOS-
correspondence by means of exact numerical simulations, when localized states
or semi-classical orbits characterize the wavefunction of the system.Comment: 8 pages, 8 figure
Scanning Gate Spectroscopy of transport across a Quantum Hall Nano-Island
We explore transport across an ultra-small Quantum Hall Island (QHI) formed
by closed quan- tum Hall edge states and connected to propagating edge channels
through tunnel barriers. Scanning gate microscopy and scanning gate
spectroscopy are used to first localize and then study a single QHI near a
quantum point contact. The presence of Coulomb diamonds in the spectroscopy
con- firms that Coulomb blockade governs transport across the QHI. Varying the
microscope tip bias as well as current bias across the device, we uncover the
QHI discrete energy spectrum arising from electronic confinement and we extract
estimates of the gradient of the confining potential and of the edge state
velocity.Comment: 13 pages, 3 figure
Imaging Electron Wave Functions Inside Open Quantum Rings
Combining Scanning Gate Microscopy (SGM) experiments and simulations, we
demonstrate low temperature imaging of electron probability density
in embedded mesoscopic quantum rings (QRs). The tip-induced
conductance modulations share the same temperature dependence as the
Aharonov-Bohm effect, indicating that they originate from electron wavefunction
interferences. Simulations of both and SGM conductance maps
reproduce the main experimental observations and link fringes in SGM images to
.Comment: new titl
Transport inefficiency in branched-out mesoscopic networks: An analog of the Braess paradox
We present evidence for a counter-intuitive behavior of semiconductor
mesoscopic networks that is the analog of the Braess paradox encountered in
classical networks. A numerical simulation of quantum transport in a two-branch
mesoscopic network reveals that adding a third branch can paradoxically induce
transport inefficiency that manifests itself in a sizable conductance drop of
the network. A scanning-probe experiment using a biased tip to modulate the
transmission of one branch in the network reveals the occurrence of this
paradox by mapping the conductance variation as a function of the tip voltage
and position.Comment: 2nd version with minor stylistic corrections. To appear in Phys. Rev.
Lett.: Editorially approved for publication 6 January 201
Short communication: Study on epilithic diatoms in the Balikli Tohma Creek (Darende/Malatya in Turkey)
Water, being the source of life, contains many life forms. The number and diversity of algae, which constitutes the first link of the food chain, affect all living things within the aquatic environment including fish. With its streams and lakes that cover an area of approximately 10000 km2, Turkey has very important internal water resources. About 135 of the wetlands within the borders of Turkey have international importance. Twelve of those have been declared as Ramsar areas (Anonymous, 2009).The structure of diatom communities has been directly linked to the physical and chemical state of water. Therefore, diatoms are used in water quality calculations and comparisons among rivers that have different morpho¬dynamics (Allan, 1995). The Water Framework Directive has established diatom communities as an indicator for stream systems besides the physico¬chemical parameters (APHA, 1985). The inert algal species that typically cover stones and hard rocks, and exist in mucilaginous and filiform masses constitute the epilithic flora. There have been many studies in Turkey on epilithic and epiphytic diatoms. Some of those studies have been on rivers whereas some have been on creeks that periodically dry up or freeze (Altuner and Gurbuz, 1988; Dere and Sivaci, 1995; Yildiz and Atici, 1996; Pala and Caglar, 2006; Pala and Caglar, 2008; Cicek and Ertan, 2015)
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