46 research outputs found
Convex hull detection of a scattering system in an inhomogeneous background
No full textA recently introduced technique allows to estimate the convex hull of a scattering system from the knowledge of the scattered electric field on an observation domain. The technique has been formulated in the case of homogeneous backgrounds. This paper, referring to 2D geometries, aims to extend the technique to inhomogeneous backgrounds. The investigation region is assumed to be characterized by two different homogeneous mediums: one containing the whole scattering system and one containing the observation domain. A numerical analysis has been carried out in order to evaluate the performances of the technique and its robustness against noise. Some representative results are here discussed
DETERMINATION OF THE CONVEX HULL OF A RADIATING SYSTEM IN A HETEROGENEOUS BACKGROUND
No full textRecently, referring to a homogeneous background, a new technique estimating the convex hull of a source/scattering system from the radiated/scattered electromagnetic field data has been presented. In this paper, the approach is extended to the inhomogeneous background case by considering the source/scattering system and the observation domain embedded in two different homogeneous media. The underlying theory has been properly reformulated to account for the refraction phenomenon arising at the electromagnetic discontinuities boundaries by considering a 2D geometry. The performances of the technique have been estimated by means of a numerical analysis whose main representative results are presented and discussed in the paper
Fast analysis of conformal aperiodic arrays on CPUs and GPUs
No full textAn approach for the fast analysis of “irregular”, i.e., of conformal, periodic or aperiodic, 2D arrays, based on the use of the p-series approach and Non-Uniform FFT (NUFFT) routines is proposed to restore the asymptotic growth of the computing time to that of few, standard FFTs. A sub-array partition strategy is also sketched and shown to further unburden the procedure and controlling the accuracy. The approach has been implemented in both, sequential and parallel codes, enabling its execution on CPUs and on cost-effective, massively parallel computing platforms as Graphic Processing Units (GPUs). Its performance in terms of computational efficiency and accuracy has been assessed also against benchmarks provided by algorithms based on fast Matrix-Vector Multiplication routines
A regression method for the power–duration relationship when both variables are subject to error
No full textPurpose: The power–duration relationship has been variously modelled, although duration must be acknowledged as the dependent variable and is supposed to represent the only source of experimental error. However, there are certain situations, namely extremely high power outputs or outdoor field conditions, in which the error in power output measurement may not remain negligible. The geometric mean (GM) regression method deals with the assumption that also the independent variable is subject to a certain amount of experimental error, but has never been utilized in this context.
Methods: We applied the GM regression method for the two- and three-parameter critical power models and tested it against the usual weighted least square (WLS) procedure with our previous published data.
Results: There were no significant differences between parameter estimates of WLS and GM. Bias and limit of agreements between the two methods were low, while correlation coefficients were high (0.85–1.00).
Conclusions: GM provided equivalent results with respect to WLS in fitting the critical power model to experimental data and for its conceptual characteristics must be preferred wherever concerns on the precision of P measurement are present, such as for in-field power meters
Effects of Water Immersion on the Internal Power of Cycling
No full textPurpose Water immersion adds additional drag and metabolic demand for limb movement with respect to air, but its effect on the internal metabolic power (Ėint) of cycling is unknown. We aimed at quantifying the increase in Ėint during underwater cycling with respect to dry conditions at different pedaling rates. Methods Twelve healthy subjects (four women) pedaled on a waterproof cycle ergometer in an experimental pool that was either empty (DRY) or filled with tap water at 30.8°C ± 0.6°C (WET). Four different pedal cadences (fp) were studied (40, 50, 60, and 70 rpm) at 25, 50, 75, and 100 W. The metabolic power at steady state was measured via open circuit respirometry, and Ėint was calculated as the metabolic power extrapolated for 0 W. Results The Ėint was significantly higher in WET than in DRY at 50, 60, and 70 rpm (81 ± 31 vs 32 ± 30 W, 167 ± 35 vs 50 ± 29 W, 311 ± 51 vs 81 ± 30 W, respectively, all P 0.99). Ėint increased with the third power of fp both in WET and DRY (R2 = 0.49 and 0.91, respectively). Conclusions Water drag increased Ėint, although limbs unloading via the Archimedes' principle and limbs shape could be potential confounding factors. A simple formula was developed to predict the increase in mechanical power in dry conditions needed to match the rate of energy expenditure during underwater cycling: 44 fp3 - 7 W, where fp is expressed in Hertz
Field sampling and field reconstruction: a new perspective
No full textWe address the problem of extracting the maximum amount of information on an electromagnetic field over a domain D-O from field sample measurements on a domain D-I, with a priori information on the source (or scatterer). The problem is faced in two steps. In the first one, the source reconstruction is dealt with by taking into account the available a priori information and the optimal probe positioning is determined as that optimizing the singular value dynamics of the involved linear radiation operator. The second step consists of reconstructing the field on D-O as that radiated by the retrieved source. An extensive numerical analysis highlights the performance of the approach
Baroreflex dynamics during the rest to exercise transient in acute normobaric hypoxia in humans
No full textPurpose We hypothesised that during a rest-to-exercise transient in hypoxia (H), compared to normoxia (N), (i) the initial baroreflex sensitivity (BRS) decrease would be slower and (ii) the fast heart rate (HR) and cardiac output (CO) response would have smaller amplitude (A(1)) due to lower vagal activity in H than N. Methods Ten participants performed three rest-to-50 W exercise transients on a cycle-ergometer in N (ambient air) and three in H (inspired fraction of O-2 = 0.11). R-to-R interval (RRi, by electrocardiography) and blood pressure profile (by photo-plethysmography) were recorded non-invasively. Analysis of the latter provided mean arterial pressure (MAP) and stroke volume (SV). CO = HRSV. BRS was calculated by modified sequence method. Results Upon exercise onset in N, MAP fell to a minimum (MAPmin) then recovered. BRS decreased immediately from 14.7 +/- 3.6 at rest to 7.0 +/- 3.0 ms mmHg(-1) at 50 W (p < 0.01). The first BRS sequence detected at 50 W was 8.9 +/- 4.8 ms mmHg(-1) (p < 0.05 vs. rest). In H, MAP showed several oscillations until reaching a new steady state. BRS decreased rapidly from 10.6 +/- 2.8 at rest to 2.9 +/- 1.5 ms mmHg(-1) at 50 W (p < 0.01), as the first BRS sequence at 50 W was 5.8 +/- 2.6 ms mmHg(-1) (p < 0.01 vs. rest). CO-A(1) was 2.96 +/- 1.51 and 2.31 +/- 0.94 l min(-1) in N and H, respectively (p = 0.06). HR-A(1) was 7.7 +/- 4.6 and 7.1 +/- 5.9 min(-1) in N and H, respectively (p = 0.81). Conclusion The immediate BRS decrease in H, coupled with similar rapid HR and CO responses, is compatible with a withdrawal of residual vagal activity in H associated with increased sympathetic drive
Fast CPU/GPU pattern evaluation of irregular arrays
No full textAn approach for the fast analysis of "irregular", i.e., of conformal, periodic or aperiodic, 2D arrays, based on the use of the p-series approach and Non-Uniform FFT (NUFFT) routines is proposed. The approach allows for modulating the computational burden depending on the array curvature and, thanks to the use of the NUFFT, the asymptotic growth of the computing time reduces to that of a few, standard FFTs. A sub-array partition strategy is also sketched and shown to further unburden the procedure and control the accuracy. The approach has been implemented in both sequential and parallel codes enabling its execution on CPUs and on cost-effective, massively parallel computing platforms like Graphic Processing Units (GPUs). Its performance in terms of computational efficiency and accuracy has been assessed by an extensive numerical analysis and also against benchmarks provided by algorithms based on fast Matrix-Vector Multiplication routines
Cardiorespiratory Responses to Exercise in Hypobaric versus Normobaric Hypoxia: A Randomized, Single-Blind, Crossover Study
No full textPurpose: There is controversy whether there are meaningful physiological differences between hypobaric (HH) and normobaric hypoxia (NH). This study aimed to compare the cardiorespiratory responses to acute HH and NH under strictly controlled conditions. We hypothesized no differences at rest and during submaximal exercise, whereas during maximal exercise, a higher maximal ventilation (V̇Emax), peripheral oxygen saturation (SpO2) and maximal oxygen consumption (V̇O2max) in HH than in NH. Methods: In a randomized, single-blind, crossover design, eight young healthy subjects (three females) were studied in an environmental chamber in which either the barometric pressure (HH) or the inspired oxygen fraction (NH) was reduced to the equivalent of ~4000 m altitude. Measurements were taken at rest, during submaximal (moderate and high intensity) and maximal cycling exercise. Results: All resting parameters were similar between HH and NH, except for a lower root mean square of the successive R-R interval differences in HH (p < 0.05). SpO2 was 2% higher in HH at all exercise intensities (p < 0.05). During submaximal exercise, minute ventilation was similar between HH and NH. However, HH yielded a 7% lower tidal volume during moderate-intensity exercise (p < 0.05) and a lower respiratory exchange ratio during high-intensity exercise (p < 0.01). V̇Emax and V̇O2max were 11% and 6% higher in HH, respectively (p < 0.01 for both). SpO2 at maximal exercise was positively correlated with V̇Emax, V̇Emax/V̇O2max and V̇O2max. Conclusions: The higher V̇O2max found in HH than in NH can be attributed to the higher V̇Emax counteracting desaturation at maximal exercise. Conversely, submaximal SpO2 improved in HH through mechanisms other than increased ventilation. These findings are likely due to respiratory muscle unloading in HH, which operated through different mechanisms depending on exercise intensity
