119 research outputs found
Bare soil moisture retrieval from multi-temporal X-band TerraSAR-X SAR images
IGARSS 2015, Milan, ITA, 26-/07/2015 - 31/07/2015International audienceThe aim of the present study is to analyze the sensitivity of X-band SAR (TerraSAR-X) signals as a function of different physical bare soil parameters (soil moisture, soil roughness), and to evaluate the accuracy of change detection approach proposed for soil moisture estimation. Firstly, we presented a brief description of our ground and satellite database. Secondly, we considered the main results of our statistical analysis of the relationships between radar and soil parameters: soil moisture and different roughness parameters (the rms height, Zs parameter, and a new roughness parameter Zg. Finally, we proposed an algorithm combing multi-temporal X-band SAR images (TerraSAR-X) with different continuous thetaprobe measurements for the retrieval of surface soil moisture at a high spatial resolution
Influence of Radar Frequency on the Relationship Between Bare Surface Soil Moisture Vertical Profile and Radar Backscatter
International audienceThe aim of this letter is to discuss the influence of radar frequency on the relationship between surface soil moisture and the nature of radar backscatter over bare soils. In an attempt to address this issue, the advanced integral equation model was used to simulate backscatter from soil surfaces with various moisture vertical profiles, for three frequency bands, namely, L, C, and X. In these computations, we investigated the influence of the vertical heterogeneity of soil moisture on the characteristics of the backscattered signals. The influence of radar frequency is clearly demonstrated. A database produced from Envisat ASAR and TerraSAR-X data, which was acquired over bare soils with in situ measurements of moisture content and ground surface roughness, was used to validate the utility of taking the soil moisture heterogeneity into account in the backscatter model
Analysis of soil texture using terrasar x-band sar
International audienceIn this paper, it is proposed to use TERRASAR-X data for analysis and estimation of soil surface texture. Our study is based on experimental campaigns carried out over a semi-arid area in North Africa. Simultaneously to TERRASAR-X radar acquisitions, ground measurements (texture, soil moisture and roughness) were made on different test fields. A strong correlation is observed between soil texture and a processed signal from two radar images, the first acquired just after a rain event and the second corresponding to dry soil conditions, acquired three weeks later. An empirical relationship is proposed for the retrieval from radar signals of clay content percent. Soil texture mapping is proposed over the study site, which includes bare soils and olive groves
Control of Local Mass Transfer in the Separated and Reattaching Flow by a Periodic Forcing
A numerical study based on the Large Eddy Simulation (LES) methodology was made of mass transfer in locally
forced turbulent separated and reattaching flow over a backward facing step. The local forcing was given to the flow
by a sinusoidally blowing /suction of the fluid into a separated shear layer. The Reynolds number was fixed at 33000
and Schmidt number at 1. The forcing frequency was varied in the range 0 St 2, where St is the Strouhal number
of forcing. The obtained results revealed the existence of an optimum forcing frequency value, St = 0.25, in terms of
the reduced reattachment length. At this frequency the mass transfer is significantly enhanced in the recirculation
zone. The influence of the frequency and the amplitude of forcing, in the maximum mass transfer positions and the
maximum Sherwood number, are analyzed
Simulation of the Periodically Perturbed Separated and Reattaching Flow over a Backward-Facing Step
In this work, the Large Eddy Simulation (LES) methodology is used to study the effects of a periodic perturbation introduced into a separated shear layer behind a backward-facing step. This study carried out by acting on the two parameters characteristics of the perturbation: frequency and amplitude. The obtained results reveal the existence of an optimum perturbation frequency value, Stp = 0.25, in terms of the reduced reattachment length. At this perturbation frequency value, we observed an increase in the vortical shedding frequency in the reattachment zone with a significant change of the structure of the flow. The value of the optimum frequency appears to be independent of the perturbation amplitude. At this frequency the maximum decrease of reattachment length is 50% and the maximum increase of vortical shedding frequency is 43 % compared to the unperturbed case
Soil texture estimation over a semiarid area using TerraSAR-X radar data
In this letter, it is proposed to use TerraSAR-X data for analysis and estimation of soil surface texture. Our study is based on experimental campaigns carried out over a semiarid area in North Africa. Simultaneously with TerraSAR-X radar acquisitions, ground measurements (texture, soil moisture, and roughness) were made on different test fields. A strong correlation is observed between soil texture and a processed signal from two radar images, with the first acquired just after a rain event and the second corresponding to dry soil conditions, acquired three weeks later. An empirical relationship is proposed for the retrieval from radar signals of clay content percent. Soil texture mapping is proposed over the study site, which includes bare soils and olive groves
Carbon nanotube-based quantum pump in the presence of superconducting lead
Parametric electron pump through superconductor-carbon-nanotube based
molecular devices was investigated. It is found that a dc current, which is
assisted by resonant Andreev reflection, can be pumped out from such molecular
device by a cyclic variation of two gate voltages near the nanotube. The pumped
current can be either positive or negative under different system parameters.
Due to the Andreev reflection, the pumped current has the double peak structure
around the resonant point. The ratio of pumped current of N-SWNT-S system to
that of N-SWNT-N system (I^{NS}/I^N) is found to approach four in the weak
pumping regime near the resonance when there is exactly one resonant level at
Fermi energy inside the energy gap. Numerical results confirm that in the weak
pumping regime the pumped current is proportional to the square of the pumping
amplitude V_p, but in the strong pumping regime the pumped current has the
linear relation with V_p. Our numerical results also predict that pumped
current can be obtained more easily by using zigzag tube than by using armchair
tube
Resonant Andreev reflections in superconductor-carbon-nanotube devices
Resonant Andreev reflection through superconductor-carbon-nanotube devices
was investigated theoretically with a focus on the superconducting proximity
effect. Consistent with a recent experiment, we find that for high transparency
devices on-resonance, the Andreev current is characterized by a large value and
a resistance dip; low-transparency off-resonance devices give the opposite
result. We also give evidence that the observed low-temperature transport
anomaly may be a natural result of Andreev reflection process
Management of neurotrauma during COVID-19: a single centre experience and lessons for the future
Introduction: Traumatic brain injury (TBI) is amongst the leading causes of morbidity and mortality worldwide. The unprecedented emergence of COVID-19 has mandated neurosurgeons to limit viral spread and spare hospital resources whilst trying to adapt management plans for TBI. We aimed to characterize how this affects decision-making on TBI management and drive strategies to cope with future expected waves.
Methods: Retrospective TBI data collection from a single tertiary referral unit was performed between: 01/04/2019 â 30/06/2019 (âPre-Epidemicâ) and 01/04/2020 â 30/06/20 (âEpidemicâ). Demographics, mechanism of injury, TBI severity, radiological findings, alcohol/anticoagulants/antiplatelets use, and management decisions were extracted.
Results: 646 TBI referrals were received in âPre-Epidemicâ (N = 317) and âEpidemicâ (N = 280) groups. There was reduction in RTA-associated TBI (14.8 vs 9.3%; p = .04) and increase in patients on anticoagulants (14.2 vs 23.6%; p = .003) in the âEpidemicâ group. Despite similarities between other TBI-associated variables, a significantly greater proportion of patients were managed conservatively in local referring units without neurosurgical services (39.1 vs 56.8%; p < .0001), predominantly constituted by mild TBI.
Conclusion: Despite COVID-19 public health measures, the burden of TBI remains eminent. Increases in local TBI management warrant vigilance from primary healthcare services to meet post-TBI needs in the community
From favorable atomic configurations to supershell structures: a new interpretation of conductance histograms
Title: From favorable atomic configurations to supershell structures: a new
interpretation of conductance histograms Authors: A. Hasmy (IVIC), E. Medina
(IVIC), P.A. Serena (CSIC,IVIC) Comments: 7 pages, 3 figures,
cond-mat.anwar.10825 Subj-class: Soft Condensed MatterComment: 7 pages, 3 figuresSubject: fput HMS.tex HMS-FIG1.ps HMS-FIG2.ps
HMS-FIG3.p
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