19,337 research outputs found
UEFI BIOS Accessibility for the Visually Impaired
People with some kind of disability face a high level of difficulty for
everyday tasks because, in many cases, accessibility was not considered
necessary when the task or process was designed. An example of this scenario is
a computer's BIOS configuration screens, which do not consider the specific
needs, such as screen readers, of visually impaired people. This paper proposes
the idea that it is possible to make the pre-operating system environment
accessible to visually impaired people. We report our work-in-progress in
creating a screen reader prototype, accessing audio cards compatible with the
High Definition Audio specification in systems running UEFI compliant firmware.Comment: 6 page
Growth of ZnO nanostructures on Si by means of plasma immersion ion implantation and deposition
Crystalline zinc oxide (ZnO) nanostructures have been grown on Si substrates by means of Plasma Based Ion Implantation and Deposition (PIII&D) at temperature of about 300 0C and in the presence of an argon glow discharge. In the process a crucible filled with small pieces of metallic zinc plays the role of the anode of the discharge itself, being polarized by positive DC voltage of about 400V. Electrons produced by thermionic emission by an oxide cathode (Ba, Sr, Ca)O impact this crucible, causing its heating and vaporization of Zn. Partial ionization of Zn atoms takes place due to collisions with plasma particles. High negative voltage pulses (7 kv/40μs/250Hz) applied to the sample holder cause the implantation of metallic zinc into Si surface, while Zn deposition happens between pulses. After annealing at 700 0C, strong UV and various visible photoluminescence bands are observed at room temperature, as well as the presence of ZnO nanoparticles. The coated surface was characterized in detail using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy. XRD indicated the presence of only ZnO peaks after annealing. The composition analysis by EDS revealed distinct Zn/O stoichiometry relation depending on the conditions of the process. AFM images showed the formation of columns in the nanoscale range. Topography viewed by SEM showed the formation of structures similar to cactus with nanothorns. Depth analysis performed by XPS indicated an increase of concentration of metallic Zn with increasing depth and the exclusive presence of ZnO for outer regions. PIII&D allowed to growing nanostructures of ZnO on Si without the need of a buffer layer
Information entropy of classical versus explosive percolation
We study the Shannon entropy of the cluster size distribution in classical as
well as explosive percolation, in order to estimate the uncertainty in the
sizes of randomly chosen clusters. At the critical point the cluster size
distribution is a power-law, i.e. there are clusters of all sizes, so one
expects the information entropy to attain a maximum. As expected, our results
show that the entropy attains a maximum at this point for classical
percolation. Surprisingly, for explosive percolation the maximum entropy does
not match the critical point. Moreover, we show that it is possible determine
the critical point without using the conventional order parameter, just
analysing the entropy's derivatives.Comment: 6 pages, 6 figure
A Measurement of the Damping Tail of the Cosmic Microwave Background Power Spectrum with the South Pole Telescope
We present a measurement of the angular power spectrum of the cosmic microwave background (CMB) using data from the South Pole Telescope (SPT). The data consist of 790 deg^2 of sky observed at 150 GHz during 2008 and 2009. Here we present the power spectrum over the multipole range 650 < ℓ < 3000, where it is dominated by primary CMB anisotropy. We combine this power spectrum with the power spectra from the seven-year Wilkinson Microwave Anisotropy Probe (WMAP) data release to constrain cosmological models. We find that the SPT and WMAP data are consistent with each other and, when combined, are well fit by a spatially flat, ΛCDM cosmological model. The SPT+WMAP constraint on the spectral index of scalar fluctuations is n_s = 0.9663 ± 0.0112. We detect, at ~5σ significance, the effect of gravitational lensing on the CMB power spectrum, and find its amplitude to be consistent with the ΛCDM cosmological model. We explore a number of extensions beyond the ΛCDM model. Each extension is tested independently, although there are degeneracies between some of the extension parameters. We constrain the tensor-to-scalar ratio to be r < 0.21 (95% CL) and constrain the running of the scalar spectral index to be dn_s /dln k = –0.024 ± 0.013. We strongly detect the effects of primordial helium and neutrinos on the CMB; a model without helium is rejected at 7.7σ, while a model without neutrinos is rejected at 7.5σ. The primordial helium abundance is measured to be Y_p = 0.296 ± 0.030, and the effective number of relativistic species is measured to be N_eff = 3.85 ± 0.62. The constraints on these models are strengthened when the CMB data are combined with measurements of the Hubble constant and the baryon acoustic oscillation feature. Notable improvements include ns = 0.9668 ± 0.0093, r < 0.17 (95% CL), and N_eff = 3.86 ± 0.42. The SPT+WMAP data show a mild preference for low power in the CMB damping tail, and while this preference may be accommodated by models that have a negative spectral running, a high primordial helium abundance, or a high effective number of relativistic species, such models are disfavored by the abundance of low-redshift galaxy clusters
Electron Fabry-Perot interferometer with two entangled magnetic impurities
We consider a one-dimensional (1D) wire along which single conduction
electrons can propagate in the presence of two spin-1/2 magnetic impurities.
The electron may be scattered by each impurity via a contact-exchange
interaction and thus a spin-flip generally occurs at each scattering event.
Adopting a quantum waveguide theory approach, we derive the stationary states
of the system at all orders in the electron-impurity exchange coupling
constant. This allows us to investigate electron transmission for arbitrary
initial states of the two impurity spins. We show that for suitable electron
wave vectors, the triplet and singlet maximally entangled spin states of the
impurities can respectively largely inhibit the electron transport or make the
wire completely transparent for any electron spin state. In the latter case, a
resonance condition can always be found, representing an anomalous behaviour
compared to typical decoherence induced by magnetic impurities. We provide an
explanation for these phenomena in terms of the Hamiltonian symmetries.
Finally, a scheme to generate maximally entangled spin states of the two
impurities via electron scattering is proposed.Comment: 19 page
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