Dirac fermion time-Floquet crystal: manipulating Dirac points

We demonstrate how to control the spectra and current flow of Dirac electrons in both a graphene sheet and a topological insulator by applying either two linearly polarized laser fields with frequencies $\omega$ and $2\omega$ or a monochromatic (one-frequency) laser field together with a spatially periodic static potential(graphene/TI superlattice). Using the Floquet theory and the resonance approximation, we show that a Dirac point in the electron spectrum can be split into several Dirac points whose relative location in momentum space can be efficiently manipulated by changing the characteristics of the laser fields. In addition, the laser-field controlled Dirac fermion band structure -- Dirac fermion time-Floquet crystal -- allows the manipulation of the electron currents in graphene and topological insulators. Furthermore, the generation of dc currents of desirable intensity in a chosen direction occurs when applying the bi-harmonic laser field which can provide a straightforward experimental test of the predicted phenomena.Comment: 9 pages, 7 figures, version that will appear in Phys. Rev.

Material Dependence of the Wire-Particle Casimir Interaction

We study the Casimir interaction between a metallic cylindrical wire and a metallic spherical particle by employing the scattering formalism. At large separations, we derive the asymptotic form of the interaction. In addition, we find the interaction between a metallic wire and an isotropic atom, both in the non-retarded and retarded limits. We identify the conditions under which the asymptotic Casimir interaction does not depend on the material properties of the metallic wire and the particle. Moreover, we compute the exact Casimir interaction between the particle and the wire numerically. We show that there is a complete agreement between the numerics and the asymptotic energies at large separations. For short separations, our numerical results show good agreement with the proximity force approximation

Heart Rate Extraction from Novel Neck Photoplethysmography Signals.

This paper demonstrates for the first time how heart rate (HR) can be extracted from novel neck photoplethysmography (PPG). A novel algorithm is presented, which when tested in neck PPG signals recorded from 9 subjects at different respiratory rates, obtained good precision with respect to gold standard ECG signals. Mean absolute error (MAE), standard deviation error (SDAE) and root-mean-square error (RMSE) resulted in 1.22, 1.54 and 1.98 beats per minute (BPM), respectively. HRneck estimation showed strong correlation (R=0.94) with reference HRECG. Good agreement between both techniques was also demonstrated by Bland-Altman analysis. The bias between mean HR paired differences was -0.16 BPM and 95% limits of agreement (LoA) were (-4.7, 4.4). Comparatively, for widely used finger PPG, errors were slightly smaller (MAE=0.38 BPM, SDAE=0.48 BPM, RMSE=0.62BPM) and the correlation with reference ECG was also very close to 1 (R=0.99). Bias of -0.04 BPM and 95% LoA (-1.5, 1.4), also showed high degree of agreement. However, these findings show the potential the neck could have as an alternative body location for wearable monitors, aiming to reduce the number of sensing sites whilst still providing access to a wide variety of physiological parameters

Jupiter as an exoplanet: UV to NIR transmission spectrum reveals hazes, a Na layer and possibly stratospheric H2O-ice clouds

Currently, the analysis of transmission spectra is the most successful technique to probe the chemical composition of exoplanet atmospheres. But the accuracy of these measurements is constrained by observational limitations and the diversity of possible atmospheric compositions. Here we show the UV-VIS-IR transmission spectrum of Jupiter, as if it were a transiting exoplanet, obtained by observing one of its satellites, Ganymede, while passing through Jupiter's shadow i.e., during a solar eclipse from Ganymede. The spectrum shows strong extinction due to the presence of clouds (aerosols) and haze in the atmosphere, and strong absorption features from CH4. More interestingly, the comparison with radiative transfer models reveals a spectral signature, which we attribute here to a Jupiter stratospheric layer of crystalline H2O ice. The atomic transitions of Na are also present. These results are relevant for the modeling and interpretation of giant transiting exoplanets. They also open a new technique to explore the atmospheric composition of the upper layers of Jupiter's atmosphere.Comment: Accepted for publication in ApJ Letter

Coulomb correlations of a few body system of spatially separated charges

A Hartree-Fock and Hartree-Fock-Bogoliubov study of a few body system of spatially separated charge carriers was carried out. Using these variational states, we compute an approximation to the correlation energy of a finite system of electron-hole pairs. This energy is shown as a function of the Coulomb coupling and the interplane distance. We discuss how the correlation energy can be used to theoretically determine the formation of indirect excitons in semiconductors which is relevant for collective phenomena such as Bose-Einstein condensation (BEC).Comment: Conference EDISON16 (2009), 4 page

High Resolution Imaging of the Magnetic Field in the central parsec of the Galaxy

We discuss a high resolution (FWHM~ 0.45 arcsec) image of the emissive polarization from warm dust in the minispiral in the Galactic Centre and discuss the implications for the magnetic field in the dusty filaments. The image was obtained at a wavelength of 12.5 microns with the CanariCam multimode mid-infrared imager on the Gran Telescopio Canarias. It confirms the results obtained from previous observations but also reveals new details of the polarization structures. In particular, we identify regions of coherent magnetic field emission at position angles of ~45 deg to the predominantly north--south run of field lines in the Northern Arm which may be related to orbital motions inclined to the general flow of the Northern Arm. The luminous stars that have been identified as bow-shock sources in the Northern Arm do not disrupt or dilute the field but are linked by a coherent field structure, implying that the winds from these objects may push and compress the field but do not overwhelm it. The magnetic field in the the low surface brightness regions in the East-West Bar to the south of SgrA* lies along the Bar, but the brighter regions generally have different polarization position angles, suggesting that they are distinct structures. In the region of the Northern Arm sampled here, there is only a weak correlation between the intensity of the emission and the degree of polarization. This is consistent with saturated grain alignment where the degree of polarization depends on geometric effects, including the angle of inclination of the field to the line of sight and superposition of filaments with different field directions, rather than the alignment efficiency.Comment: 9 pages, 3 figures, Proceedings of Cosmic Dust X, held in Mitaka, Japan in August 201

A robust post-processing method to determine skin friction in turbulent boundary layers from the velocity profile

The present paper describes a method to extrapolate the mean wall shear stress, , and the accurate relative position of a velocity probe with respect to the wall, Δ, from an experimentally measured mean velocity profile in a turbulent boundary layer. Validation is made between experimental and direct numerical simulation data of turbulent boundary layer flows with independent measurement of the shear stress. The set of parameters which minimize the residual error with respect to the canonical description of the boundary layer profile is taken as the solution. Several methods are compared, testing different descriptions of the canonical mean velocity profile (with and without overshoot over the logarithmic law) and different definitions of the residual function of the optimization. The von Kármán constant is used as a parameter of the fitting process in order to avoid any hypothesis regarding its value that may be affected by different initial or boundary conditions of the flow. Results show that the best method provides an accuracy of Δ≤0.6% for the estimation of the friction velocity and Δ+≤0.3 for the position of the wall. The robustness of the method is tested including unconverged near-wall measurements, pressure gradient, and reduced number of points; the importance of the location of the first point is also tested, and it is shown that the method presents a high robustness even in highly distorted flows, keeping the aforementioned accuracies if one acquires at least one data point in +<10. The wake component and the thickness of the boundary layer are also simultaneously extrapolated from the mean velocity profile. This results in the first study, to the knowledge of the authors, where a five-parameter fitting is carried out without any assumption on the von Kármán constant and the limits of the logarithmic layer further from its existence

A low-voltage low-power front-end for wearable EEG systems

A low-voltage and low-power front-end for miniaturized, wearable EEG systems is presented. The instrumentation amplifier, which removes the electrode drift and conditions the signal for a 10-bit A/D converter, combines a chopping strategy with quasi-FGMOS (QFG) transistors to minimize low frequency noise whilst enabling operation at 1 V supply. QFG devices are also key to the A/D converter operating at 1.2 V with 70dB of SNR and an oversampling ratio of 64. The whole system consumes less than 2uW at 1.2V.Published versio