177 research outputs found
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
Long dephasing time and high temperature ballistic transport in an InGaAs open quantum dot
We report on measurements of the magnetoconductance of an open circular
InGaAs quantum dot between 1.3K and 204K. We observe two types of
magnetoconductance fluctuations: universal conductance fluctuations (UCFs), and
'focusing' fluctuations related to ballistic trajectories between openings. The
electron phase coherence time extracted from UCFs amplitude is larger than in
GaAs/AlGaAs quantum dots and follows a similar temperature dependence (between
T^-1 and T^-2). Below 150K, the characteristic length associated with
'focusing' fluctuations shows a slightly different temperature dependence from
that of the conductivity.Comment: 6 pages, 4 figures, proceedings of ICSNN2002, to appear in Physica
Imaging and controlling electron transport inside a quantum ring
Traditionally, the understanding of quantum transport, coherent and
ballistic1, relies on the measurement of macroscopic properties such as the
conductance. While powerful when coupled to statistical theories, this approach
cannot provide a detailed image of "how electrons behave down there". Ideally,
understanding transport at the nanoscale would require tracking each electron
inside the nano-device. Significant progress towards this goal was obtained by
combining Scanning Probe Microscopy (SPM) with transport measurements2-7. Some
studies even showed signatures of quantum transport in the surrounding of
nanostructures4-6. Here, SPM is used to probe electron propagation inside an
open quantum ring exhibiting the archetype of electron wave interference
phenomena: the Aharonov-Bohm effect8. Conductance maps recorded while scanning
the biased tip of a cryogenic atomic force microscope above the quantum ring
show that the propagation of electrons, both coherent and ballistic, can be
investigated in situ, and even be controlled by tuning the tip potential.Comment: 11 text pages + 3 figure
Analyse génétique comparée de 19 formes recombinantes VIH-1 inter-groupes M et O et impact évolutif
International audienc
Circulation of human influenza viruses and emergence of Oseltamivir-resistant A(H1N1) viruses in Cameroon, Central Africa
<p>Abstract</p> <p>Background</p> <p>While influenza surveillance has increased in most developing countries in the last few years, little influenza surveillance has been carried out in sub-Saharan Africa and no information is available in Central Africa. The objective of this study was to assess the prevalence of influenza viruses circulating in Yaounde, Cameroon and determine their antigenic and genetic characteristics.</p> <p>Methods</p> <p>Throat and/or nasal swabs were collected from November 2007 to October 2008 from outpatients with influenza-like illness (ILI) in Yaounde, Cameroon and analyzed by two different techniques: a one-step real time reverse transcription-polymerase chain reaction (RT-PCR) and virus isolation in MDCK cells. Typing and subtyping of virus isolates was performed by hemagglutination inhibition (HI), and viruses were sent to the WHO Collaborating Centre in London, UK for further characterization and analyses of antiviral resistance by enzyme inhibition assay and nucleotide sequencing.</p> <p>Results</p> <p>A total of 238 patients with ILI were sampled. During this period 70 (29%) samples were positive for influenza by RT-PCR, of which only 26 (11%) were positive by virus isolation. By HI assay, 20 of the 26 isolates were influenza type A (10 H3N2 and 10 H1N1) and 6 were influenza type B (2 B/Victoria/2/87 lineage and 4 B/Yagamata/16/88 lineage). Seven (70%) of the H1N1 isolates were shown to be resistant to oseltamivir due to a H275Y mutation.</p> <p>Conclusions</p> <p>This study confirmed the circulation of influenza A(H1N1), A(H3N2) and B viruses in the human population in Central Africa and describes the emergence of oseltamivir-resistant A(H1N1) viruses in Central Africa.</p
Nanotechnology : the Next Industrial Revolution ?
The essence of nanotechnology is the ability to work at the molecular level, atom by atom, to create large structures with fundamentally new properties. Nanostructures offer a new paradigm for materials manufacture by submicron-scale self-organization and self-assembly to create entities from the “bottom up” rather than the “top down” method. Nanometer structures will foster a revolution not only in information technology hardware but also in advances healthcare, therapeutics, diagnostics, environment and energy
The USS Greeneville collision: a discussion of crisis communication : a directed research project ...
This paper is a discussion of crisis communication in order to gain a better understanding of the U.S. Navy's crisis communications actions after the submarine collided with the Japanese fishing boat. This paper will analyze the crisis management performance of the U.S. Navy throughout the crisis. This study is organized into 6 chapters: Chapter 1 provides an overview of the accident. Chapter 2 is a review of the scholarly literature on crisis communication theory. Chapter 3 provides a methodology for the case study. Chapter 4 analyzes the Navy's crisis communications performance per scholarly theory. Chapter 5 is a discussion of the U.S. Navy's crisis communication performance. Chapter 6 provides a summary and suggestions for future research.http://archive.org/details/theussgreenevill109451104
Low frequency noise conversion in fets under nonlinear operation
Based upon the active line concept, the conversion mechanisms of microscopic low frequency noise (e.g. generation-recombination noise) located in the channel of a Field Effect Transistor (FET) which is driven by a large RF signal is demonstrated. The first consequence is that the based band (low frequency) input gate noise voltage spectral density is dependent on the magnitude of the input RF power applied to the FET. Moreover, the microscopic generation-recombination noise sources located in the channel are responsible of up-converted input gate noise voltage spectral density around the RF frequency
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