462 research outputs found
Assessment of the conservation status of natural and semi-natural patches associated with urban areas through habitat suitability indices
Urban environments rely on the surrounding natural ecosystems remnants as providers of ecosystem functions, therefore these areas not only support a unique biodiversity but also have a social value for maintaining public health and wellbeing. For this reason, urbanization is considered to be one the biggest threats to ecosystems, leading to native biodiversity simplification and, thus, to a detriment of the provided ecosystem services. Moreover, this change in land use results in high levels of landscape fragmentation and modification in areas surrounding the habitat remnants which, in consequence, become inadequate for many native species. In this context, it is important that urban planners have the information to assess the possible consequences of future changes in land use in order to increase the landscape chances of supporting both, native biodiversity and the needs of a growing human population. The objective of the present work is to evaluate the ecological integrity of natural and semi-natural vegetation patches immersed in an urban area in order to generate a conceptual framework for landscape assessment that allows urban planners to envision the best choice for city development at a given place. To do so, we developed a quantitative integral environmental evaluation index that includes ecological characterization, geological characterization, and environmental characterization (presence of anthropic disturbance) of the assessed area. We conclude that the index we have generated in this work is suitable to be used as a management tool to allow an unbiased valuation and to identify managing situations that require a short term response.Fil: Natale, Evangelina Sandra. Fundación Conservación y Desarrollo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Villalba, G.. Fundación Conservación y Desarrollo; ArgentinaFil: Junquera, J. E.. Fundación Conservación y Desarrollo; ArgentinaFil: Zalba, Sergio Martín. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia. Grupo de Estudios en Conservación y Manejo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Evidence of magnetic field quenching of phosphorous-doped silicon quantum dots
We present data on the electrical transport properties of highly-doped
silicon-on-insulator quantum dots under the effect of pulsed magnetic fields up
to 48 T. At low field intensities, B<7 T, we observe a strong modification of
the conductance due to the destruction of weak localization whereas at higher
fields, where the magnetic field length becomes comparable to the effective
Bohr radius of phosphorous in silicon, a strong decrease in conductance is
demonstrated. Data in the high and low electric field bias regimes are then
compared to show that close to the Coulomb blockade edge magnetically-induced
quenching to single donors in the quantum dot is achieved at about 40 T.Comment: accepted for publication at Current Applied Physic
Electric-field tuning of the valley splitting in silicon corner dots
We perform an excited state spectroscopy analysis of a silicon corner dot in
a nanowire field-effect transistor to assess the electric field tunability of
the valley splitting. First, we demonstrate a back-gate-controlled transition
between a single quantum dot and a double quantum dot in parallel that allows
tuning the device in to corner dot formation. We find a linear dependence of
the valley splitting on back-gate voltage, from to with a slope of (or equivalently a slope
of with respect to the effective field). The
experimental results are backed up by tight-binding simulations that include
the effect of surface roughness, remote charges in the gate stack and discrete
dopants in the channel. Our results demonstrate a way to electrically tune the
valley splitting in silicon-on-insulator-based quantum dots, a requirement to
achieve all-electrical manipulation of silicon spin qubits.Comment: 5 pages, 3 figures. In this version: Discussion of model expanded;
Fig. 3 updated; Refs. added (15, 22, 32, 34, 35, 36, 37
A silicon-based single-electron interferometer coupled to a fermionic sea
We study Landau-Zener-Stueckelberg-Majorana (LZSM) interferometry under the
influence of projective readout using a charge qubit tunnel-coupled to a
fermionic sea. This allows us to characterise the coherent charge qubit
dynamics in the strong-driving regime. The device is realised within a silicon
complementary metal-oxide-semiconductor (CMOS) transistor. We first read out
the charge state of the system in a continuous non-demolition manner by
measuring the dispersive response of a high-frequency electrical resonator
coupled to the quantum system via the gate. By performing multiple fast
passages around the qubit avoided crossing, we observe a multi-passage LZSM
interferometry pattern. At larger driving amplitudes, a projective measurement
to an even-parity charge state is realised, showing a strong enhancement of the
dispersive readout signal. At even larger driving amplitudes, two projective
measurements are realised within the coherent evolution resulting in the
disappearance of the interference pattern. Our results demonstrate a way to
increase the state readout signal of coherent quantum systems and replicate
single-electron analogues of optical interferometry within a CMOS transistor
Charge dynamics and spin blockade in a hybrid double quantum dot in silicon
Electron spin qubits in silicon, whether in quantum dots or in donor atoms,
have long been considered attractive qubits for the implementation of a quantum
computer due to the semiconductor vacuum character of silicon and its
compatibility with the microelectronics industry. While donor electron spins in
silicon provide extremely long coherence times and access to the nuclear spin
via the hyperfine interaction, quantum dots have the complementary advantages
of fast electrical operations, tunability and scalability. Here we present an
approach to a novel hybrid double quantum dot by coupling a donor to a
lithographically patterned artificial atom. Using gate-based rf reflectometry,
we probe the charge stability of this double quantum dot system and the
variation of quantum capacitance at the interdot charge transition. Using
microwave spectroscopy, we find a tunnel coupling of 2.7 GHz and characterise
the charge dynamics, which reveals a charge T2* of 200 ps and a relaxation time
T1 of 100 ns. Additionally, we demonstrate spin blockade at the inderdot
transition, opening up the possibility to operate this coupled system as a
singlet-triplet qubit or to transfer a coherent spin state between the quantum
dot and the donor electron and nucleus.Comment: 6 pages, 4 figures, supplementary information (3 pages, 4 figures
Reconfigurable quadruple quantum dots in a silicon nanowire transistor
We present a novel reconfigurable metal-oxide-semiconductor multi-gate
transistor that can host a quadruple quantum dot in silicon. The device consist
of an industrial quadruple-gate silicon nanowire field-effect transistor.
Exploiting the corner effect, we study the versatility of the structure in the
single quantum dot and the serial double quantum dot regimes and extract the
relevant capacitance parameters. We address the fabrication variability of the
quadruple-gate approach which, paired with improved silicon fabrication
techniques, makes the corner state quantum dot approach a promising candidate
for a scalable quantum information architecture
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