832 research outputs found
Effects of thickness on the spin susceptibility of the 2D electron gas
Using available quantum Monte Carlo predictions for a strictly 2D electron
gas, we have estimated the spin susceptibility of electrons in actual devices
taking into account the effect of the finite transverse thickness and finding a
very good agreement with experiments. A weak disorder, as found in very clean
devices and/or at densities not too low, just brings about a minor enhancement
of the susceptibility.Comment: 4 pages, 3 figure
Self-sustained vibrations in volcanic areas extracted by Independent Component Analysis: a review and new results
We investigate the physical processes associated with volcanic tremor and explosions. A volcano is a complex system where a fluid source interacts with the solid edifice so generating seismic waves in a regime of low turbulence. Although the complex behavior escapes a simple universal description, the phases of activity generate stable (self-sustained) oscillations that can be described as a non-linear dynamical system of low dimensionality. So, the system requires to be investigated with non-linear methods able to individuate, decompose, and extract the main characteristics of the phenomenon. Independent Component Analysis (ICA), an entropy-based technique is a good candidate for this purpose. Here, we review the results of ICA applied to seismic signals acquired in some volcanic areas. We emphasize analogies and differences among the self-oscillations individuated in three cases: Stromboli (Italy), Erebus (Antarctica) and Volcán de Colima (Mexico). The waveforms of the extracted independent components are specific for each volcano, whereas the similarity can be ascribed to a very general common source mechanism involving the interaction between gas/magma flow and solid structures (the volcanic edifice). Indeed, chocking phenomena or inhomogeneities in the volcanic cavity can play the same role in generating self-oscillations as the languid and the reed do in musical instruments. The understanding of these background oscillations is relevant not only for explaining the volcanic source process and to make a forecast into the future, but sheds light on the physics of complex systems developing low turbulence
Statistical analysis of Stromboli VLP tremor in the band [0.1?0.5] Hz: some consequences for vibrating structures
International audienceWe analyze time series of Strombolian volcanic tremor, focusing our attention on the frequency band [0.1?0.5] Hz (very long period (VLP) tremor). Although this frequency band is largely affected by noise, we evidence two significant components by using Independent Component Analysis with the frequencies, respectively, of ~0.2 and ~0.4 Hz. We show that these components display wavefield features similar to those of the high frequency Strombolian signals (>0.5 Hz). In fact, they are radially polarised and located within the crater area. This characterization is lost when an enhancement of energy appears. In this case, the presence of microseismic noise becomes relevant. Investigating the entire large data set available, we determine how microseismic noise influences the signals. We ascribe the microseismic noise source to Scirocco wind. Moreover, our analysis allows one to evidence that the Strombolian conduit vibrates like the asymmetric cavity associated with musical instruments generating self-sustained tones
Spin Susceptibility of Interacting Two-dimensional Electrons with Anisotropic Effective Mass
We report measurements of the spin susceptibility in dilute (rs up to 10)
AlAs two-dimensional (2D) electrons occupying a single conduction-band valley
with an anisotropic in-plane Fermi contour, characterized by longitudinal and
transverse effective masses, ml and mt. As the density is decreased, the spin
susceptibility is significantly enhanced over its band value, reflecting the
role of interaction. Yet the enhancement is suppressed compared to the results
of quantum Monte Carlo based calculations that take the finite thickness of the
electron layer into account but assume an isotropic effective mass equal to
sqrt(ml.mt). Proper treatment of an interacting 2D system with an anisotropic
effective mass therefore remains a theoretical challenge.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev.
Validation of the Internet Gaming Disorder Scale - Short-Form (IGDS9-SF) in an Italian-speaking sample
Background and aims: The inclusion of Internet Gaming Disorder (IGD) in Section III of the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders has increased the interest of researchers in the development of new standardized psychometric tools for the assessment of such a disorder. To date, the nine-item Internet Gaming Disorder Scale - Short-Form (IGDS9-SF) has only been validated in English, Portuguese, and Slovenian languages. Therefore, the aim of this investigation was to examine the psychometric properties of the IGDS9-SF in an Italian-speaking sample. Methods: A total of 757 participants were recruited to the present study. Confirmatory factor analysis and multi-group analyses were applied to assess the construct validity. Reliability analyses comprised the average variance extracted, the standard error of measurement, and the factor determinacy coefficient. Convergent and criterion validities were established through the associations with other related constructs. The receiver operating characteristic curve analysis was used to determine an empirical cut-off point. Results: Findings confirmed the singlefactor structure of the instrument, its measurement invariance at the configural level, and the convergent and criterion validities. Satisfactory levels of reliability and a cut-off point of 21 were obtained. Discussion and conclusions: The present study provides validity evidence for the use of the Italian version of the IGDS9-SF and may foster research into gaming addiction in the Italian context
The effect of various after-ripening temperature regimens on the germination behaviour of Ambrosia artemisiifolia
Correlation Energy and the Spin Susceptibility of the Two-Valley Two-dimensional Electron Gas
We find that the spin susceptibility of a two-dimensional electron system
with valley degeneracy does not grow critically at low densities, at variance
with experimental results [A. Shashkin et al., Phys. Rev. Lett. 96, 036403
(2006)]. We ascribe this apparent discrepancy to the weak disorder present in
experimental samples. Our prediction is obtained from accurate correlation
energies computed with state of-the-art diffusion Monte Carlo simulations and
fitted with an analytical expression which also provides a local spin density
functional for the system under investigation.Comment: 7 pages, 3 figures, accepted for publication in Phys. Rev.
A statistical study of the Stromboli volcano explosion quakes before and during 2002-2003 eruptive crisis
We study the seismic wavefield and the statistical properties of the Stromboli volcano
explosions preceding and during the 2002–2003 crisis. We analyze the recordings of a
three‐component seismometer operating since 23 May 2002 to 30 January 2003, including
the first 34 days of the crisis. Before the crisis, we recognize three bell‐shaped classes of
spectra with maxima falling in the range 1–5 Hz. Spectral content has two main changes, the
most prominent one occurring at the crisis onset when the frequency peak at ∼0.3 Hz
increases in amplitude. Independent component analysis extracts three time‐stable
independent oscillations that peaked at 1.1, 1.8, and 2.5 Hz, with radial and shallow
polarization indicating a stable source mechanism. Energy of the explosions is lognormally
distributed, except during a 2 month time interval before the crisis when it also shows a
higher mean value. The interoccurrence time distributions display an homogeneous
Poissonian behavior with a mean intertime of 250 s, without changes at the crisis onset. Only
swarms of explosions are not ruled by a Poisson process and display higher occurrence rates
and higher energies. Finally, we depict a scheme of the crisis. A modification of the
equilibrium is induced by rising magma that produces a change in the boundary conditions of
the plumbing system. The escape from the equilibrium produces, at first, variations in the
usual statistics of the explosions, then it leads to the lava effusion and to a pressure drop in
the plumbing system that induces a deep gas slug nucleation and the excitation of low
frequencies
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