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Biomedical subjects

A Patanè

Publications and source records attributed to A Patanè.

11 recordsLinked to original sources
PubMed2006

Strong effect of resonant impurities on Landau-level quantization.

We investigate experimentally the effect of a random distribution of nitrogen (N) impurities on the Landau-level spectrum of a GaAs quantum well. Our magnetotunneling study reveals complex and nonequally spaced Landau levels and a quenching of the Landau states at a well-defined bias and electron energy which is resonant with that of the N atoms. Analysis of the magnetic field dependence of the tunnel current into the Landau levels of the well also provides quantitative information about the nonresonant component of the N-related scattering potential.

Journal Article↗
PubMed2004

Magnetic-field-induced suppression of electronic conduction in a superlattice.

We use a magnetic field applied along the axis of a semiconductor superlattice (SL) as a controllable means of creating a one-dimensional band structure. We demonstrate that the current flow through the SL is strongly suppressed when the electron motion perpendicular to the SL axis is strongly confined by the quantizing magnetic field. By modeling this behavior using semiclassical and nonequilibrium Green's function methods, we show that the observed quenching arises from a qualitative change in electron dynamics caused by increasing quantum confinement.

Journal Article↗
PubMed2004

Chaotic electron diffusion through stochastic webs enhances current flow in superlattices.

Understanding how complex systems respond to change is of fundamental importance in the natural sciences. There is particular interest in systems whose classical newtonian motion becomes chaotic as an applied perturbation grows. The transition to chaos usually occurs by the gradual destruction of stable orbits in parameter space, in accordance with the Kolmogorov-Arnold-Moser (KAM) theorem--a cornerstone of nonlinear dynamics that explains, for example, gaps in the asteroid belt. By contrast, 'non-KAM' chaos switches on and off abruptly at critical values of the perturbation frequency. This type of dynamics has wide-ranging implications in the theory of plasma physics, tokamak fusion, turbulence, ion traps, and quasicrystals. Here we realize non-KAM chaos experimentally by exploiting the quantum properties of electrons in the periodic potential of a semiconductor superlattice with an applied voltage and magnetic field. The onset of chaos at discrete voltages is observed as a large increase in the current flow due to the creation of unbound electron orbits, which propagate through intricate web patterns in phase space. Non-KAM chaos therefore provides a mechanism for controlling the electrical conductivity of a condensed matter device: its extreme sensitivity could find applications in quantum electronics and photonics.

Journal Article↗
PubMed2003

Magnetotunneling spectroscopy of dilute Ga(AsN) quantum wells.

We use magnetotunneling spectroscopy to explore the admixing of the extended GaAs conduction band states with the localized N-impurity states in dilute GaAs(1-y)N(y) quantum wells. In our resonant tunneling diodes, electrons can tunnel into the N-induced E- and E+ subbands in a GaAs(1-y)N(y) quantum well layer, leading to resonant peaks in the current-voltage characteristics. By varying the magnetic field applied perpendicular to the current direction, we can tune an electron to tunnel into a given k state of the well; since the applied voltage tunes the energy, we can map out the form of the energy-momentum dispersion curves of E- and E+. The data reveal that for a small N content (approximately 0.1%) the E- and E+ subbands are highly nonparabolic and that the heavy effective mass E+ states have a significant Gamma-conduction band character even at k=0.

Journal Article↗
PubMed2000

Imaging the electron wave function in self-assembled quantum dots.

Magnetotunneling spectroscopy is used as a noninvasive and nondestructive probe to produce two-dimensional spatial images of the probability density of an electron confined in a self-assembled semiconductor quantum dot. The technique exploits the effect of the classical Lorentz force on the motion of a tunneling electron and can be regarded as the momentum (k) space analog of scanning tunneling microscopy imaging. The images reveal the elliptical symmetry of the ground state and the characteristic lobes of the higher energy states.

Journal Article↗
PubMed1996

Changes in respiratory drive account for the magnitude of dyspnoea during bronchoconstriction in asthmatics.

To evaluate whether the interindividual differences in dyspnoea perceived by asthmatic subjects for the same level of airway narrowing could depend on different changes in respiratory drive, we assessed the relationship between changes in airway calibre, changes in neuromuscular output, and dyspnoea rate during progressive bronchoconstriction induced by methacholine. We studied 18 asymptomatic asthmatic subjects (aged 18-36 yrs; 11 males and 7 females) with normal lung function. Dyspnoea (Borg scale), mouth occlusion pressure (P0.1), and forced expiratory volume in one second (FEV1) were measured at baseline and after inhalation of aerosols of doubling concentrations of methacholine (MCh). The progressive bronchoconstriction induced by MCh was associated with a progressive increase both of P0.1 and dyspnoea. Dyspnoea score was linearly related either to the fall in FEV1, or to the increase in P0.1. However, the slope values of the relationship between dyspnoea score and the corresponding percent fall in FEV1 showed a large interindividual variability (0.05-0.32; coefficient of variability (CoV) 43%). By contrast, the slope values of the relationship between dyspnoea score and the corresponding percent increase in P0.1 ranged 0.02-0.05 (CoV = 14%), indicating a more homogeneous response to dyspnoea for the same change in P0.1. At the highest MCh concentration, the dyspnoea score was linearly related to the corresponding change in P0.1 (r = 0.91; p < 0.01), but not to the corresponding percentage fall in FEV1 (r = 0.28). These results show that the interindividual differences in dyspnoea perceived by asthmatic subjects for the same level of airway narrowing are associated with different changes in respiratory drive during bronchoconstriction.

Adolescent↗