Anatomical and functional brain approach along short abrupt changes in G-levels

To conduct experiments under abrupt changes in g-levels, a single-engine aerobatic aircraft has been used, providing 6-8 seconds of reduced gravity, preceded and followed by 5-7 seconds of hypergravity periods. Due to the specific conditions of the flight and previous findings [1], the hypothesis of the present work lies on the idea that some sensory inputs could have a notorious effect on brain final responses when gravity is altered. Therefore, this study focuses on the evaluation of such hypothesis, based on the analysis of the evolution in time of intracranial activity of limbic, visual and auditory cortices. Five subjects (N=5, age 41¿14 years) have flown in parabolic flight with their eyes both open and closed. Electroencephalogram signals were recorded with an Emotive Epoc headset, synchronized with a triaxial accelerometer. The intracranial brain bioelectric activity (standardized current density) throughout the parabola, was calculated by applying Standard Low Resolution Brain Electromagnetic Tomography, and it was analyzed for the limbic, visual and auditory cortices. Intracranial activity of the Temporal, Parietal and Occipital lobes were carried out as well in order to compare the different periods/phases of the flight. Results detected a lower brain activity during the hypogravity phase in all lobes and cortices, only in the case of open eyes. The bioelectrical brain activity along the parabola showed similar patterns in all lobes and cortices, when visual inputs are highlighted. Suppressing the sight, two major behaviors were detected in brain activity: one for temporal lobe and auditory cortex, and second one for the rest of the lobes and visual cortex. It Seemed that, flying with closed eyes, other sensory stimuli were enhanced, in this case the auditory cortex. To confirm the validity of the results two-way ANOVA (factors lobe/phases) and Fisher post hoc test have been applied on mean intracranial activity values in all cases. Spectral entropy evolution in time has been considered as a fast indicator of the sudden extracranial brain activity variation during short g-changes. For open eyes, spectral entropy values indicated a slight decrease at the onset of the hypogravity phase, whereas in case of closed eyes, this change was detected in the last seconds of the parabola, even though these fluctuations were statistically non-significant. Results suggest that some of the sensory inputs can indeed have an impact on brain final response, when gravity conditions are altered.Peer ReviewedPostprint (published version

Brain activity changes induced by open and closed eyes during low-g maneuvers

The present work reports and discuses the changes in brain bioelectrical signals induced on normal subjects by open and closed eyes during their first parabolic flight in a small aerobatic plane. A parabolic flight maneuver is characterized by gravity changes from 1g to ~3g (first hypergravity phase, P1) to ~0.05g (hypogravity phase, P2) to ~ 2g (second hypergravity phase, P3) to 1g (inflight phase, B1). EEG signals have been obtained using a 14 channels EMOTIV EPOC device. Digital preprocessing techniques have been applied in order to properly clean all the experimental signals. Standardized Low Resolution Brain Electromagnetic Tomography (sLORETA) allowed obtaining intracranial activity. Statistical analysis of this intracranial activity was performed by using analysis of variance techniques (ANOVA). If ANOVA results were significant, post-hoc analyses were carried out. The results clearly show a decreasing of the intracranial activity during the hypogravity phase with open and closed eyes. Concerning mean values, significant differences have been detected between the hypogravity, P2, and both hypergravity phases, P1 and P3. Significant differences have also been detected for open eyes, by lobes. To check if intracranial activity presents significant differences along the phases, Even Related Potential, ERP, analyses were carried out. For both open and closed eyes tests, sLORETA images show statistical significant differences in the Brodmann areas 18 (Left Occipital Lobe) and 39 (Right Temporal Lobe) between B1-P2, respectively.Postprint (published version

On the determination of diffusion coefficients in two-component alloys and doped semiconductors: several implications concerning the International Space Station

The accurate determination of mass diffusion coefficients is a technologically relevant problem that has implications on the modelling and control of material processes such as crystal growth and casting. It is also important in the validation of different theories of atomic diffusion. The experimental determination of these coefficients, when there is a liquid phase, is difficult due to the unavoidable presence of buoyancy driven convection currents that enhance mass transport and disturb diffusion measurements. To minimize as much as possible these problems, long capillaries are used in order to confine the fluid and reduce the intensity of the convective motions. These measurements have also been done in reduced gravity environments, but the residual gravity may still be able to induce buoyancy driven convection motions. The aim of our work is to analyze the impact of low solutal Rayleigh number environments on the accuracy of the interdiffusion coefficient measurements using long capillaries. In the present study we deal with two liquid systems; photovoltaic silicon and Al-based liquid binary alloys at high temperature. We have numerically simulated two different experimental techniques used to determine the diffusion coefficients; the shear cell and the long capillary techniques. We also consider the effect of rotating the cylindrical cell along their axis as a mechanism to reduce axial convective transport even in Earth laboratories. Finally, we use typical accelerometric signals from the International Space Station (ISS) in the quasi-steady range of frequencies. The signals concentrate on typical station reboosts because the accelerometric level of the rest of potentially dangerous disturbances - dockings, undockings and Extra Vehicular Activities, EVAs - is considerably lower.Peer ReviewedPostprint (author's final draft

Efficient tunable laser operation of Tm:KGd(WO4)2 in the continuous-wave regime at room temperature

Tm:KGd(WO/sub 4/)/sub 2/ is studied as a three-level laser on the /sup 3/F/sub 4/ /spl rarr/ /sup 3/H/sub 6/ transition and a tunable source in the 2-/spl mu/m spectral range, operating at room temperature. An overall tunability extending from 1790 to 2042 nm is achieved with maximum output powers of 400 mW for an absorbed pump power of 1 W. Various doping levels, pump wavelengths and polarization configurations are compared and the advantages of the monoclinic double tungstates over other Tm-hosts are outlined

Brain activity changes induced by open and closed eyes during low-g maneuvers

The present work reports and discuses the changes in brain bioelectrical signals induced on normal subjects by open and closed eyes during their first parabolic flight in a small aerobatic plane. A parabolic flight maneuver is characterized by gravity changes from 1g to ~3g (first hypergravity phase, P1) to ~0.05g (hypogravity phase, P2) to ~ 2g (second hypergravity phase, P3) to 1g (inflight phase, B1). EEG signals have been obtained using a 14 channels EMOTIV EPOC device. Digital preprocessing techniques have been applied in order to properly clean all the experimental signals. Standardized Low Resolution Brain Electromagnetic Tomography (sLORETA) allowed obtaining intracranial activity. Statistical analysis of this intracranial activity was performed by using analysis of variance techniques (ANOVA). If ANOVA results were significant, post-hoc analyses were carried out. The results clearly show a decreasing of the intracranial activity during the hypogravity phase with open and closed eyes. Concerning mean values, significant differences have been detected between the hypogravity, P2, and both hypergravity phases, P1 and P3. Significant differences have also been detected for open eyes, by lobes. To check if intracranial activity presents significant differences along the phases, Even Related Potential, ERP, analyses were carried out. For both open and closed eyes tests, sLORETA images show statistical significant differences in the Brodmann areas 18 (Left Occipital Lobe) and 39 (Right Temporal Lobe) between B1-P2, respectively

Image processing of cylinder wake generation

In the present study, image processing techniques are applied to the chronophotographic visualizations of a cylinder wake generation. The flow patterns obtained by means of tracer particles are digitalized and processed in order to characterize the flow. This characterization is carried out by determining the evolution of the geometric parameters governing the wake, together with the streamfunction, vorticity, and pressure distributions. The present study reaches the moment of shedding of the first pair of vortices

Onsite vibrational characterization of DCMIX2/3 experiments

The SODI-DCMIX thermodiffusion series experiments are part of the fluid research program carried out by the European Space Agency on board of the International Space Station (ISS). In particular, DCIMIX2/3 were conducted in the past inside the Microgravity Science Glovebox in the US Laboratory. Due to the physical nature of the processes implied, these kind of runs were very long and particularly delicate because the low vibratory limit requirements must be maintained for hours. This restrictive condition not always is achieved, therefore, an accurate surveillance of the acceleration levels along the different experiments is necessary, to ensure a correct interpretation of the experimental results. This work analyzes onsite vibrational environment of DCMIX2/3 covering the periods in which the experiments were going on. To do so, acceleration signals only coming from the es03 sensor, nearest to the experimental equipment and located in the Glovebox, were downloaded from the PIMS NASA website. To be as precise as possible the signals have always been treated minute by minute. To detect the transient disturbances along the experiments, several warnings were considered. First, 1 min RMS values, for the three acceleration components were evaluated, in time and in frequency domain. Additional information was obtained by plotting the power spectral densities of the signals, PSD, and their spectrogram with the aim of characterizing long periods of acceleration data. Due to great influence of low frequencies in this type of experiments, the Frequency Factor Index, FFI, was evaluated each minute. Complementary, the spectral entropy evolution was proposed as a fast new indicator of external perturbations. It has been found a good correlation between the spectrogram, temporal RMS and spectral entropy. Finally, a graphic representation of the points associated to the 1-min RMS values in one-third-octave frequency intervals which exceed the ISS limit curve requirements, was considered as a new and easy strategy for depicting the warnings that recognize the main disturbances along the experiment.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Vortex shedding from a spinning cylinder

An experimental investigation of a two-dimensional turbulent wake behind a spinning cylinder at Re=9000 is carried out to determine the influence of the rotation on the initial development of the flow. Spectral analysis of the velocity data measured in the near wake shows that for peripheral velocities up to the value of the free¿stream velocity, a distinct Kármán vortex activity exists within the wake, whereas for greater peripheral velocities, the Kármán activity deteriorates and disappears for values in excess of twice the free-stream velocity

Vortex shedding from a spinning cylinder

An experimental investigation of a two-dimensional turbulent wake behind a spinning cylinder at Re=9000 is carried out to determine the influence of the rotation on the initial development of the flow. Spectral analysis of the velocity data measured in the near wake shows that for peripheral velocities up to the value of the free¿stream velocity, a distinct Kármán vortex activity exists within the wake, whereas for greater peripheral velocities, the Kármán activity deteriorates and disappears for values in excess of twice the free-stream velocity

Green luminescence of Er3+ in stoichiometric KYb(WO4)2 single crystals

We grew good-optical-quality KYb~WO4)2 single crystals doped with erbium ions by the top seeded solution growth slow cooling method. Optical absorption of erbium was performed at room temperature ~RT! and at 6 K. Green photoluminescence of erbium was achieved at RT and 6 K after selective excitation of ytterbium ions at 940 nm (10 638 cm21). The splitting of all found excited energy levels and the ground energy level of erbium in KYb~WO4)2 is presented derived from the accurate absorption and emission measurements, respectively. The lifetime of the Stokes and the anti-Stokes green emissions of erbium were measured after excitation at 488 nm (20 490 cm21) and 940 nm(10 638 cm21), respectively. We propose applying the up-conversion model to the observed green emission