194 research outputs found
Manifestation of geometric resonance in current dependence of AC susceptibility for unshunted array of Nb-AlOx-Nb Josephson junctions
A pronounced resonance-like structure has been observed in the current
dependence of AC susceptibility for two-dimensional array of unshunted
Nb-AlOx-Nb Josephson junctions. Using a single-plaquette approximation, we were
able to successfully fit our data assuming that resonance structure is related
to the geometric (inductive) properties of the array.Comment: to appear in Physica C (in press
Universal R-C crossover in current-voltage characteristics for unshunted array of overdamped Nb-AlO_x-Nb Josephson junctions
We report on some unusual behavior of the measured current-voltage
characteristics (CVC) in artificially prepared two-dimensional unshunted array
of overdamped Nb-AlO_x-Nb Josephson junctions. The obtained nonlinear CVC are
found to exhibit a pronounced (and practically temperature independent)
crossover at some current I_{cr}=\left(\frac{1}{2\beta_C}-1\right)I_C from a
resistance R dominated state with V_R=R\sqrt{I^2-I_C^2} below I_{cr} to a
capacitance C dominated state with V_C=\sqrt{\frac{\hbar}{4eC}} \sqrt{I-I_C}
above I_{cr}. The origin of the observed behavior is discussed within a
single-plaquette approximation assuming the conventional RSJ model with a
finite capacitance and the Ambegaokar-Baratoff relation for the critical
current of the single junction
Subtransmission overhead lines mechanical monitoring for fast detection of damaging events
Different harmful events affecting high voltage overhead lines (OHLs) cause changes in the mechanical tension (tensile strength) of conductors. A mechanical monitoring of OHLs, therefore, can provide useful additional information (compared with the information provided by the widely used SCADA systems) about the power system state. The tension measurements combined with a few environmental measurements (air temperature, wind speed) can be used for an automatic (fast) detection of different events and for their approximate location along an OHL, reducing the impact of these events. Referring to 132-150 kV sub-transmission OHLs, this paper proposes some original algorithms, based on the mechanical monitoring of OHLs, for the automatic detection of the following events: conductor breaking, fall of trees on the conductors, ice/snow sleeve accretion on the conductors, strands breaking and galloping. The proposed algorithms require a limited number of sensors placed along the OHLs for measurements of the conductor tension and weather-related quantities
Unveiling the mono-rhamnolipid and di-rhamnolipid mechanisms of action upon plasma membrane models
Rhamnolipids (RLs) are biosurfactants with significant tensioactive and emulsifying properties. They are mainly composed by mono-RL and di-RL components. Although there are numerous studies concerning their molecular properties, information is scarce regarding the mechanisms by which each of the two components interacts with cell membranes. Herein, we performed phase-contrast and fluorescence microscopy experiments on plasma membrane models represented by giant-unilamellar-vesicles (GUVs) composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 2-[[(E,2S,3R)-1,3-dihydroxy-2-(octadecanoylamino) octadec-4-enyl]peroxy-hydroxyphosphoryl]oxyethyl-trimethylazanium (sphingomyelin, SM) and (3ÎČ)-cholest-5-en-3-ol (cholesterol, CHOL) (1:1:1 M ratio), which present liquid-order (Lo) liquid-disorder (Ld) phase coexistence, in the presence of either mono-RL or di-RL in 0.06â0.25 mM concentration range. A new method has been developed to determine area and volume of GUVs with asymmetrical shape and a kinetic model describing GUV-RL interaction in terms of two mechanisms, RL-insertion and pore formation, has been worked out. Results show that the insertion of mono-RL in the membrane outer leaflet is the dominant process with no pore formation and a negligible effect in modifying membrane permeability, but induces lipid mixing. Conversely, the di-RL-GUV interaction begins with the insertion mechanism and, as the time passes by, the pore formation process occurs. The analyses of di-RL show that the whole process is only relevant in the Ld phase with a higher extent to 0.25 mM than to 0.06 mM
Magnetically controlled exciton transfer in hybrid quantum dot-quantum well nanostructures
A magnetophotoluminescence study of the carrier transfer with hybrid
InAs/GaAs quantum dot(QD)-InGaAs quantum well (QW) structures is carried out
where we observe an unsual dependence of the photoluminescence (PL) on the GaAs
barrier thickness at strong magnetic field and excitation density. For the case
of a thin barrier the QW PL intensity is observed to increase at the expense of
a decrease in the QD PL intensity. This is attributed to changes in the
interplane carrier dynamics in the QW and the wetting layer (WL) resulting from
increasing the magnetic field along with changes in the coupling between QD
excited states and exciton states in the QW and the WL
Aharonov-Bohm interference in quantum ring exciton: effects of built-in electric fields
We report a comprehensive discussion of quantum interference effects due to
the finite structure of excitons in quantum rings and their first experimental
corroboration observed in the optical recombinations. Anomalous features that
appear in the experiments are analyzed according to theoretical models that
describe the modulation of the interference pattern by temperature and built-in
electric fields.Comment: 6 pages, 7 figure
Morphological, electrical and optical properties of Si-doped GaAs grown by MBE on GaAs non-(100)-oriented substrates
The incorporation and amphoteric behavior of Si has been investigated in molecular beam epitaxy (MBE) GaAs samples grown on (311)A, (211)A and (111)A substrates at different growth conditions. Hall effect measurements have revealed that the doping changes from p- to n-type when the V4/III flux ratio is increased and the growth temperature is decreased. The transition flux ratio is lower for the (211)A than for the (311)A surfaces. Photoluminescence measurements have shown that, when the V4/III flux ratio is increased or the growth temperature is decreased, arsenic vacancy defects are changed into pairs of Ga vacancy and Ga antisite defects. These results are explained by considering the kinetics of the MBE growth process and the orientation dependence of the surface bonding
Electrical control of glass-like dynamics in vanadium dioxide for data storage and processing
Metalâoxideâsemiconductor junctions are the building blocks of modern electronics and can provide a variety of functionalities, from memory to computing. The technology, however, faces constraints in terms of further miniaturization and compatibility with postâvon Neumann computing architectures. Manipulation of structuralârather than electronicâstates could provide a path to ultrascaled low-power functional devices, but the electrical control of such states is challenging. Here we report electronically accessible long-lived structural states in vanadium dioxide that can provide a scheme for data storage and processing. The states can be arbitrarily manipulated on short timescales and tracked beyond 10,000âs after excitation, exhibiting features similar to glasses. In two-terminal devices with channel lengths down to 50ânm, sub-nanosecond electrical excitation can occur with an energy consumption as small as 100âfJ. These glass-like functional devices could outperform conventional metalâoxideâsemiconductor electronics in terms of speed, energy consumption and miniaturization, as well as provide a route to neuromorphic computation and multilevel memories
Contributions des tradipraticiens de santĂ© au traitement antirĂ©troviral : Ătude de cas Ă Nampula, Mozambique
Contexte: LâĂ©pidĂ©mie du virus de lâimmunodĂ©ficience humaine au Mozambique est un problĂšme grave de santĂ© publique et le MinistĂšre de la SantĂ© a Ă©tendu le traitement antirĂ©troviral Ă tous les districts du pays. Cependant, on constate un nombre Ă©levĂ© dâabandon du traitement encore insuffisamment Ă©valuĂ©. LâOrganisation Mondiale de la SantĂ© recommande que les tradipraticiens de santĂ© collaborent avec les systĂšmes nationaux de santĂ© dans les pays en dĂ©veloppement, pour combattre cette Ă©pidĂ©mie, mais il existe peu dâactions dans ce domaine Ă ce jour.
Objectif: Ăvaluer la connaissance des tradipraticiens sur lâinfection et leur disponibilitĂ© Ă coopĂ©rer avec les services de santĂ© dans la Province de Nampula au Mozambique, pour amĂ©liorer les rĂ©sultats du traitement antirĂ©troviral.
Lieux: Cinq centres de santĂ© des districts de la Province de Nampula, au Nord du Mozambique, avec des taux Ă©levĂ©s dâincidence du virus dâimmunodĂ©ficience humaine et dâabandon du traitement.
Méthodes: Une étude mixte transversale, utilisant des interviews ciblés et des discussions de groupes focaux. Les données quantitatives étaient traitées par fréquence et les données qualitatives par analyse de discours et ethnographie locale.
RĂ©sultats: Nous avons interviewĂ© 79 tradipraticiens de santĂ©. La perte de poids Ă©tait souvent considĂ©rĂ©e comme le signal principal de suspicion dâinfection par le virus dâimmunodĂ©ficience humaine et certains tradipraticiens ne pas les signes de la maladie ; la majoritĂ© pensait que les antirĂ©troviraux amĂ©liorent la qualitĂ© de vie des patients, ne prĂ©tendait pas traiter lâinfection, savait quâelle nâest pas curable, avait une idĂ©e sur le concept de bonne adhĂ©sion au traitement et rĂ©fĂ©rait les cas compliquĂ©s au centre de santĂ©. En ce qui concerne lâalimentation, la moitiĂ© considĂ©rait exclusivement les cĂ©rĂ©ales comme lâaliment principal ; les fruits Ă©taient importants pour un quart ; lâeau potable est ignorĂ©e. La majoritĂ© Ă©tait prĂȘte Ă collaborer avec le systĂšme de santĂ© et avait des propositions de coopĂ©ration pratique : la qualification et la reconnaissance individuelle et la formation intĂ©grĂ©e avec les professionnels de santĂ©.
Conclusion: Les tradipraticiens connaissaient lâinfection par le virus dâimmunodĂ©ficience humaine et les facteurs associĂ©s, mais il y a des lacunes. Ils ont signalĂ© quâils utilisaient principalement les plantes mĂ©dicinales, ce qui peut contribuer au traitement des infections opportunistes et la majoritĂ© rĂ©fĂ©rait dĂ©jĂ des patients au centre de santĂ© ; mais la collaboration nĂ©cessite une procĂ©dure Ă©ducative et une articulation structurĂ©e. Les lacunes de connaissance empĂȘchent une coopĂ©ration efficace dans le combat contre lâĂ©pidĂ©mie. Le groupe est disponible pour coopĂ©rer avec le systĂšme de santĂ© pour amĂ©liorer les rĂ©sultats du traitement antirĂ©troviral, mais pour ça il est nĂ©cessaire dâinformer et former les tradipraticiens dans un processus intĂ©grĂ© de collaboration avec les professionnels de santĂ© conventionnels
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