2,306 research outputs found
Electronic transport through a parallel--coupled triple quantum dot molecule: Fano resonances and bound states in the continuum
The electronic transport through a triple quantum dot molecule attached in
parallel to leads in presence of a magnetic flux is studied. Analytical
expressions of the linear conductance and density of states for the molecule in
equilibrium at zero temperature are obtained. As a consequence of quantum
interference, the conductance exhibits in general a Breit--Wigner and two Fano
resonances, the positions and widths of which are controlled by the magnetic
field. Every two flux quanta, there is an inversion of roles of the bonding and
antibonding states. For particular values of the magnetic flux and dot-lead
couplings, one or even both Fano resonances collapse and bound states in the
continuum (BIC's) are formed. The line broadenings of the molecular states are
examined as a function of the Aharonov--Bohm phase around the condition for the
formation of BIC's, finding resonances extremely narrow and robust against
variations of the magnetic field.Comment: 15 pages, 7 figure
Rate-dependent propagation of cardiac action potentials in a one-dimensional fiber
Action potential duration (APD) restitution, which relates APD to the
preceding diastolic interval (DI), is a useful tool for predicting the onset of
abnormal cardiac rhythms. However, it is known that different pacing protocols
lead to different APD restitution curves (RCs). This phenomenon, known as APD
rate-dependence, is a consequence of memory in the tissue. In addition to APD
restitution, conduction velocity restitution also plays an important role in
the spatiotemporal dynamics of cardiac tissue. We present new results
concerning rate-dependent restitution in the velocity of propagating action
potentials in a one-dimensional fiber. Our numerical simulations show that,
independent of the amount of memory in the tissue, waveback velocity exhibits
pronounced rate-dependence and the wavefront velocity does not. Moreover, the
discrepancy between waveback velocity RCs is most significant for small DI. We
provide an analytical explanation of these results, using a system of coupled
maps to relate the wavefront and waveback velocities. Our calculations show
that waveback velocity rate-dependence is due to APD restitution, not memory.Comment: 17 pages, 7 figure
Transformation elastodynamics and active exterior acoustic cloaking
This chapter consists of three parts. In the first part we recall the
elastodynamic equations under coordinate transformations. The idea is to use
coordinate transformations to manipulate waves propagating in an elastic
material. Then we study the effect of transformations on a mass-spring network
model. The transformed networks can be realized with "torque springs", which
are introduced here and are springs with a force proportional to the
displacement in a direction other than the direction of the spring terminals.
Possible homogenizations of the transformed networks are presented, with
potential applications to cloaking. In the second and third parts we present
cloaking methods that are based on cancelling an incident field using active
devices which are exterior to the cloaked region and that do not generate
significant fields far away from the devices. In the second part, the exterior
cloaking problem for the Laplace equation is reformulated as the problem of
polynomial approximation of analytic functions. An explicit solution is given
that allows to cloak larger objects at a fixed distance from the cloaking
device, compared to previous explicit solutions. In the third part we consider
the active exterior cloaking problem for the Helmholtz equation in 3D. Our
method uses the Green's formula and an addition theorem for spherical outgoing
waves to design devices that mimic the effect of the single and double layer
potentials in Green's formula.Comment: Submitted as a chapter for the volume "Acoustic metamaterials:
Negative refraction, imaging, lensing and cloaking", Craster and Guenneau
ed., Springe
Coupled dynamics of voltage and calcium in paced cardiac cells
We investigate numerically and analytically the coupled dynamics of
transmembrane voltage and intracellular calcium cycling in paced cardiac cells
using a detailed physiological model and its reduction to a three-dimensional
discrete map. The results provide a theoretical framework to interpret various
experimentally observed modes of instability ranging from electromechanically
concordant and discordant alternans to quasiperiodic oscillations of voltage
and calcium
Ionospheric perturbations in possible association with the 2010 Haiti earthquake, as based on medium-distance subionospheric VLF propagation data
Ionospheric perturbations in possible association with the 2010 Haiti earthquake occurred on 12 January 2010 (with a magnitude of 7.0 and depth of 10 km) are investigated on the basis of subionospheric propagation data from the NAA transmitter on the east coast of the USA to a VLF receiving station in Peru. The local nighttime VLF amplitude data are extensively investigated during the period from the beginning of October 2009 to the end of March 2010, in which the trend (nighttime average amplitude), dispersion and nighttime fluctuation are analysed. It is found that a clear precursory ionosphere perturbation is detected just around New Years day of 2010, about 12 days before the main shock, which is characterised by the simultaneous decrease in the trend and the increases in dispersion and nighttime fluctuation. An additional finding might be the presence of the effect of the Earth's tide one and two months before the main shock, which can only be seen for a huge EQ
Descritores morfológicos e agronômicos para a caracterização de mandioca (Manihot esculenta Crantz).
Esse documento teve por objetivo relatar o resultado da reunião Latino-americana sobre recursos genéticos de mandioca realizada pelo Centro Nacional Mandioca e Fruticultura Tropical, da EMBRAPA, em parceria com o Centro Internacional de Agricultura Tropical (CIAT), em Cruz das Almas, Bahia, Brasil no ano de 1995. Participaram desta reunião especialistas em recursos genéticos de mandioca da Argentina, Brasil, Colômbia, Cuba, Equador, Guatemala e Paraguai. Atualizou-se e padronizou-se os descritores morfológicos e agronômicos disponíveis para mandioca e de seus respectivos estados, utilizados na caracterização e avaliação dos acessos mantidos em coleções de germoplasma localizados na América Latina. Ficou estabelecido que os acessos de mandioca deveriam serem caracterizados de forma padronizada mediante o uso de setenta e cinco descritores morfológicos e agronômicos, discriminados neste documento, classificados em cinco categorias de acordo com a ordem de importância ou finalidade de utilização.bitstream/item/81576/1/Descritores-morfologicos-Wania-Fukuda-Documentos-78-1998.pd
Transport through a quantum wire with a side quantum-dot array
A noninteracting quantum-dot array side-coupled to a quantum wire is studied.
Transport through the quantum wire is investigated by using a noninteracting
Anderson tunneling Hamiltonian. The conductance at zero temperature develops an
oscillating band with resonances and antiresonances due to constructive and
destructive interference in the ballistic channel, respectively. Moreover, we
have found an odd-even parity in the system, whose conductance vanishes for an
odd number of quantum dots while becomes for an even number. We
established an explicit relation between this odd-even parity, and the
positions of the resonances and antiresonances of the conductivity with the
spectrum of the isolated QD arrayComment: 5 pages, 4 figures, submitted to PR
Morphological and biochemical indicators of Fusarium oxysporum f sp. fragariae in strawberry crops (Fragaria x ananassa Duch) in the province of Pichincha, Ecuador
ArticleFusarium oxysporum f. sp. fragariae is a fungal pathogen, transmitted by soil in crops of strawberry (Fragaria x ananassa Duch.), which causes wilt disease that, kill the strawberry cultivars. The disease caused by Fusarium oxysporum f. sp., fragariae is hard to detect as the of the symptoms are similar with other soil-borne diseases. In spite of detection methods targeted F. oxysporum using molecular criteria have been developed, they have not been shown to successfully identity the unique identity of F. oxysporum strain that causes this disease. In Ecuador, the cultivation of strawberry has acquired great importance for the consumption, promoting the increase of its production. However, the process of importing plant material from producing countries for the purpose of improving production has contributed to the spread of the fungus. The objective of this study was to identify the presence of the Fusarium oxysporum f. sp fragariae by means of morphometric identification and the application of biochemical methods (BIOLOG) in the province of Pichincha. Fifty-two diseased strawberry plants and 52 asymptomatic plants were analyzed. Of these, 13 isolates were identified by morphometry as F. oxysporum. However, through BIOLOG four strains were identified as F. oxysporum, 5 as Fusarium sp., 2 F. lateritium, 1 F. udum and 1 strain as F. sacchari. The results obtained through the identification and evaluation confirmed the presence of F. oxysporum f. sp., fragariae in evaluated strawberry cultivars, thus determining the high risk to exist if the pathogen spreads in new plantations in Ecuador
Change of Scale and Forecasting with the Control-Function Method in Logit Models
Endogeneity is a model misspecification that precludes the consistent estimation of the model parameters. The control-function method is the most suitable tool to address endogeneity for several discrete choice models that are relevant in transportation research. However, the estimators obtained with the control-function method are consistent only up to a scale. In this paper, we first depict the determinants of this change of scale by adapting an existing result for omitted orthogonal attributes in logit models. Then, we study the problem of forecasting under these circumstances. We show that a procedure proposed in previous literature may lead to significant biases, and we suggest novel alternatives to be used with synthetic populations. We use Monte Carlo experimentation and real data on residential location choice to illustrate these results. The paper finishes by summarizing the findings of this investigation and suggesting future lines of research in this area.MIT-Portugal Progra
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