The potential of micro-electro-mechanical accelerometers in human vibration measurements

This paper evaluates the advantages and the drawbacks deriving from the use of MEMS (micro-electro-mechanical systems) accelerometers for hand-arm and whole-body vibration measurements. Metrological performances of different transducers were assessed through the identification of their frequency response function, linearity, floor noise and sensitivity to thermal and electromagnetic disturbances. Experimental results highlighted a standard instrumental uncertainty (including the nonlinearity) lower than 5% with the single frequency calibration procedure, such a value was reduced to 2%. The temperature effect was negligible and the electromagnetic disturbances sensitivity was comparable to that of the piezoelectric accelerometers. The compatibility of measurements obtained with MEMS accelerometers with those of piezoelectric-based measurement chains was verified for two specific applications. An example of direct transducer fixation on the skin for vibration transmissibility measurements is also presented. Thanks to the MEMS peculiarities – mainly small sizes and low cost – since novel approaches in the vibration monitoring could be pursued. For instance, it is possible to include by design MEMS accelerometers in any hand-held tool at the operator interface, or inside the seats structures of cars, tractors and trucks. This could be a viable solution to easily obtain repeatable exposure measurements and could also provide diagnostic signals for the tools or seats of functional monitoring.     

Simultaneous near field imaging of electric and magnetic field in photonic crystal nanocavities

The insertion of a metal-coated tip on the surface of a photonic crystal microcavity is used for simultaneous near field imaging of electric and magnetic fields in photonic crystal nanocavities, via the radiative emission of embedded semiconductor quantum dots (QD). The photoluminescence intensity map directly gives the electric field distribution, to which the electric dipole of the QD is coupled. The magnetic field generates, via Faraday's law, a circular current in the apex of the metallized probe that can be schematized as a ring. The resulting magnetic perturbation of the photonic modes induces a blue shift, which can be used to map the magnetic field, within a single near-field scan.     

Anti-deuterons from heavy Dark Matter

We study the fluxes of anti-deuterons that could be produced by annihilations in the galactic halo of Dark Matter particles with multi-TeV mass and a large annihilation cross section, as indicated by the recent PAMELA results. The model of Minimal Dark Matter (MDM) is an example in this category. We find that the fluxes are well within the reach of planned experiments for DM candidates that annihilate mainly into quark pairs, and also extend into the multi-GeV range above the expected astrophysical background. They are instead less promising if the main annihilation channel is into gauge bosons.     

Optimizing ICA in fMRI using information on spatial regularities of the sources

Spatial independent component analysis (ICA) is a well-established technique for multivariate analysis of functional magnetic resonance imaging (fMRI) data. It blindly extracts spatiotemporal patterns of neural activity from functional measurements by seeking for sources that are maximally independent. Additional information on one or more sources (e.g., spatial regularity) is often available; however, it is not considered while looking for independent components. In the present work, we propose a new ICA algorithm based on the optimization of an objective function that accounts for both independence and other information on the sources or on the mixing model in a very general fashion. In particular, we apply this approach to fMRI data analysis and illustrate, by means of simulations, how inclusion of a spatial regularity term helps to recover the sources more effectively than with conventional ICA. The improvement is especially evident in high noise situations. Furthermore we employ the same approach on data sets from a complex mental imagery experiment, showing that consistency and physiological plausibility of relatively weak components are improved.     

Noise estimation in single- and multiple-coil magnetic resonance data based on statistical models

Noise estimation is a challenging task in magnetic resonance imaging (MRI), with applications in quality assessment, filtering or diffusion tensor estimation. Main noise estimators based on the Rician model are revisited and classified in this article, and new useful methods are proposed. Additionally, all the surveyed estimators are extended to the noncentral chi model, which applies to multiple-coil MRI and some important parallel imaging algorithms for accelerated acquisitions. The proposed new noise estimation procedures, based on the distribution of local moments, show better performance in terms of smaller variance and unbiased estimation over a wide range of experiments, with the additional advantage of not needing to explicitly segment the background of the image.     

Origin of the X‐ray magnetic circular dichroism at the L‐edges of the rare‐earths in RxR1−x′Al2 systems

An X‐ray magnetic circular dichroism (XMCD) study performed at the rare‐earth L_2,3‐edges in the R_xR_1?x′Al₂ compounds is presented. It is shown that both R and R′ atoms contribute to the XMCD recorded at the L‐edges of the selected rare‐earth, either R or R′. The amplitude of the XMCD signal is not directly correlated to the magnetization or to the value of the individual (R, R′) magnetic moments, but it is related to the molecular field acting on the rare‐earth tuned in the photoabsorption process. This result closes a longstanding study of the origin of the XMCD at the L‐edge of the rare‐earths in multi‐component systems, allowing a full understanding of the exact nature of these signals.     

Cytogenetics of four Omophoita species (Coleoptera,Chrysomelidae, Alticinae): A comparative analysis using mitotic and meiotic cells submitted to the standard staining and C-banding technique

Omophoita belongs to the tribe Oedionychini and is endemic from Neotropical region. The species of the tribe Oedionychini have revealed certain singular chromosomal features, such as sex chromosomes with extremely large size, asynapsis, and synthelic or amphithelic orientation during meiosis. Additionally, some species also showed post-reductional segregation of the gigantic sex chromosomes in meiotic division. The purpose of this work was to characterize cytogenetically four Omophoita species (O. magniguttis, O. octoguttata, O. personata, and O. sexnotata) in relation to their diploid number, chromosomal morphology, type of sex chromosome system, and constitutive heterochromatin pattern in mitotic and meiotic cells, and compare the obtained data with those of related species to establish the mechanism involved in the chromosomal differentiation of these species during the evolutionary process. The diploid number, 2n = 22 = 20 + X + y, and meiotic formulae, 10II + X + y, observed in these species were similar to those of the same genus and other species related. The autosomal morphology was acrocentric in O. magniguttis and O. octoguttata, metacentric in O. personata, and predominantly metacentric in O. sexnotata. In all these species, the sex chromosomes were metacentric. The secondary constriction occurred in pair 6 and X chromosome of O. personata, and in pair 6 and y chromosome of O. sexnotata. The constitutive heterochromatin was pericentromeric in O. magniguttis and centromeric in O. sexnotata, with the exception of the mitotic sex chromosomes of O. sexnotata, in which centromeric C band was lacking. Additional C bands in the sex chromosomes of O. magniguttis and certain autosomes and sex chromosomes of O. sexnotata were observed. Collochores were indirectly identified in the spermatocytes of O. octoguttata, O. personata, and O. sexnotata. The main mechanisms involved in the karyotype evolution of these species were discussed.     

Not All Fluorescent Nanodiamonds Are Created Equal: A Comparative Study

Fluorescent nanodiamonds (FNDs) are vital to many emerging nanotechnological applications, from bioimaging and sensing to quantum nanophotonics. Yet, understanding and engineering the properties of fluorescent defects in nanodiamonds remain challenging. The most comprehensive study to date is presented, of the optical and physical properties of five different nanodiamond samples, in which fluorescent nitrogen‐vacancy (NV) centers are created using different fabrication techniques. The FNDs' fluorescence spectra, lifetime, and spin relaxation time (T₁) are investigated via single‐particle confocal fluorescence microscopy and in ensemble measurements in solution (T₁ excepted). Particle sizes and shapes are determined using scanning electron microscopy and correlated with the optical results. Statistical tests are used to explore correlations between the properties of individual particles and also analyze average results to directly compare different fabrication techniques. Spectral unmixing is used to quantify the relative NV charge‐state (NV^? and NV⁰) contributions to the overall fluorescence. A strong variation is found and quantified in the properties of individual particles within all analyzed samples and significant differences between the different particle types. This study is an important contribution toward understanding the properties of NV centers in nanodiamonds. It motivates new approaches to the improved engineering of NV‐containing nanodiamonds for future applications.     

Paraxial designing of planar waveguide variable-index focusing elements: Part 1—lenses of circular symmetry

A paraxial ray equation is used to evaluate refractive index profiles for a family of radially symmetric planar waveguide lenses. Two cases are considered: the (theoretically) full-aperture solution, and the solution with smooth index variation (non-full-aperature case). In deriving the latter case a new method has been applied that consists of the proper choice of a continuous deflection function. Both types of index profiles are described by exceptionally simple formulas.     

Gravitational and electromagnetic signatures of accretion into a charged black hole

We present the derivation and the solutions to the coupled electromagnetic and gravitational perturbations with sources in a charged black hole background. We work in the so called ghost gauge and consider as source of the perturbations the infall of radial currents. In this way, we study a system in which it is provoked a response involving both, gravitational and electromagnetic waves, which allows us to analyze the dependence between them. We solve numerically the wave equations that describe both signals, characterize the waveforms and study the relation between the input parameters of the infalling matter with those of the gravitational and electromagnetic responses.