111 research outputs found
GaAs delta-doped quantum wire superlattice characterization by quantum Hall effect and Shubnikov de Haas oscillations
Quantum wire superlattices (1D) realized by controlled dislocation slipping
in quantum well superlattices (2D) (atomic saw method) have already shown
magnetophonon oscillations. This effect has been used to investigate the
electronic properties of such systems and prove the quantum character of the
physical properties of the wires. By cooling the temperature and using pulsed
magnetic field up to 35 T, we have observed both quantum Hall effect (QHE) and
Shubnikov de Haas (SdH) oscillations for various configurations of the magnetic
field. The effective masses deduced from the values of the fundamental fields
are coherent with those obtained with magnetophonon effect. The field rotation
induces a change in the resonance frequencies due to the modification of the
mass tensor as in a (3D) electron gas. In view the QHE, the plateaus observed
in rho_yz are dephased relatively to rho_zz minima which seems to be linked to
the dephasing of the minima of the density of states of the broadened Landau
levels
Charge Detection in Phosphorus-doped Silicon Double Quantum Dots
We report charge detection in degenerately phosphorus-doped silicon double
quantum dots (DQD) electrically connected to an electron reservoir. The sensing
device is a single electron transistor (SET) patterned in close proximity to
the DQD. Measurements performed at 4.2K show step-like behaviour and shifts of
the Coulomb Blockade oscillations in the detector's current as the reservoir's
potential is swept. By means of a classical capacitance model, we demonstrate
that the observed features can be used to detect single-electron tunnelling
from, to and within the DQD, as well as to reveal the DQD charge occupancy.Comment: 4 pages, 3 figure
Optimized minigaps for negative differential resistance creation in strongly delta-doped (1D) superlattices
The "atomic saw method" uses the passage of dislocations in two-dimensional
(2D) quantum-well superlattices to create periodic slipping layers and
one-dimensional (1D) quantum wire superlattices. The effects of this space
structuring of the samples on the allowed energies are analysed in the case of
GaAs d-doped superlattices. If they are sufficiently large, the various
minigaps appearing in the 1D band structure could be responsible for the
presence of negative differential resistance (NDR) with high critical current
in these systems. The purpose is to determine the evolution of the minigaps in
terms of the sample parameters and to obtain the means to determine both the 2D
and 1D structural characteristics where NDR could appear.Comment: see erratum 10.1006/spmi.1998.070
Study and characterization by magnetophonon resonance of the energy structuring in GaAs/AlAs quantum-wire superlattices
We present the characterization of the band structure of GaAs/AlAs
quantum-wire 1D superlattices performed by magnetophonon resonance with pulsed
magnetic fields up to 35 T. The samples, generated by the "atomic saw method"
from original quantum-well 2D superlattices, underwent substantial
modifications of their energy bands built up on the X-states of the bulk. We
have calculated the band structure by a finite element method and we have
studied the various miniband structures built up of the masses m_t and m_l of
GaAs and AlAs at the point X. From an experimental point of view, the main
result is that in the 2D case we observe only resonances when the magnetic
field B is applied along the growth axis whereas in the 1D case we obtain
resonances in all magnetic field configurations. The analysis of the maxima (or
minima for B // E) in the resistivity rho_xy as a function of B allows us to
account, qualitatively and semi-quantitatively, for the band structure
theoretically expected
Amplified fragment length polymorphism genotyping of metronidazole-resistant Helicobacter pylori infecting dyspeptics in England
ObjectiveIntra-specific diversity of Helicobacter pylori infecting stomachs of different individuals was investigated by numerical analysis of amplified fragment length polymorphisms (AFLP), to determine the existence of clones within the strain population and the effect that antibiotic treatment, particularly with metronidazole (Mtz), had on the balance of types/subtypes present before and after treatment.MethodsThe 92 cultures studied comprised 89 single or multiple (pre- and post-treatment) isolates from gastric biopsies from 35 dyspeptic patients at two geographical locations in England, and three reference strains. HindIII restriction fragments tagged with specific adaptors were used as template DNA for AFLP. Patterns were coded in binary format according to deduced sizes of amplified fragments, and numerical analysis was performed.ResultsH. pylori isolated from different individuals were highly diverse (43 AFLP types) with a continuum of similarities that included three putative strain clusters at the 55% similarity level. Twelve sets each comprised identical isolates but subclonal variants with similarities of 82-99% coexisted in isolate sets from 19 patients. Seven sets contained strains with different AFLP types which for several corresponded with vacA/cagA genotypic differences. Mtz resistance was a feature of clonal as well as unrelated isolates.ConclusionsAFLP profiling was a robust, reproducible and highly discriminatory means of indexing H. pylori strain diversity, and the numerical analysis enabled clonal/subclonal variants infecting an individual to be defined and contrasted with the general species diversity. The majority (65%) of patients had co-infections with different strain types/subtypes but antibiotic treatment apparently did not markedly modify H. pylori population diversity in individual stomachs. Mtz sensitivity was generally associated with greater strain diversity as several subtypes often coexisted in sensitive pretreatment strain sets. In contrast, Mtz-resistant strain populations were less diverse, which was attributed to selection by previous exposure to nitroimidazoles in the same or a different host
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
Activation mechanisms in sodium-doped Silicon MOSFETs
We have studied the temperature dependence of the conductivity of a silicon
MOSFET containing sodium ions in the oxide above 20 K. We find the impurity
band resulting from the presence of charges at the silicon-oxide interface is
split into a lower and an upper band. We have observed activation of electrons
from the upper band to the conduction band edge as well as from the lower to
the upper band. A possible explanation implying the presence of Hubbard bands
is given.Comment: published in J. Phys. : Condens. Matte
Design and Experimental Validation of a Software-Defined Radio Access Network Testbed with Slicing Support
Network slicing is a fundamental feature of 5G systems to partition a single
network into a number of segregated logical networks, each optimized for a
particular type of service, or dedicated to a particular customer or
application. The realization of network slicing is particularly challenging in
the Radio Access Network (RAN) part, where multiple slices can be multiplexed
over the same radio channel and Radio Resource Management (RRM) functions shall
be used to split the cell radio resources and achieve the expected behaviour
per slice. In this context, this paper describes the key design and
implementation aspects of a Software-Defined RAN (SD-RAN) experimental testbed
with slicing support. The testbed has been designed consistently with the
slicing capabilities and related management framework established by 3GPP in
Release 15. The testbed is used to demonstrate the provisioning of RAN slices
(e.g. preparation, commissioning and activation phases) and the operation of
the implemented RRM functionality for slice-aware admission control and
scheduling
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