Search results for "Sip"

FPGA based digital lock-in amplifier for fNIRS systems

2018

Lock-In Amplifiers (LIA) represent a powerful technique helping to improve signals detectability when low signal to noise ratios are experienced. Continuous Wave functional Near Infrared Spectroscopy (CW-fNIRS) systems for e-health applications usually suffer of poor detection due to the presence of strong attenuations of the optical recovering path and therefore small signals are severely dipped in a high noise floor. In this work a digital LIA system, implemented on a Zynq® Field Programmable Gate Array (FPGA), has been designed and tested to verify the quality of the developed solution, when applied in fNIRS systems. Experimental results have shown the goodness of the proposed solutions.

Study of the multipactor phenomenon using a full-wave integral equation technique

2017

Abstract Multipactor effect is a well-known phenomenon of RF breakdown in satellite payloads which degrades components, generates undesirable harmonics, contributes to power dissipation and increases noise in communications. Traditionally, multipactor has been investigated with the aim of obtaining the so-called multipactor threshold voltage, or to present different multipaction detection methods. However, very little attention has been focused on analysing this phenomenon using a multimodal approach. The main goal of this work is to analyse the interaction between a multipactor current and a realistic microwave cavity by means of a rigorous and accurate formulation. For the first time to t…

Dissipative analogies of step-pool features: From rills to mountain streams

2019

Abstract In this paper the dissipative similarity of step-pool units at different spatial scales ranging from rills to streams is analyzed. This investigation benefits from the latest theoretical advances in open channel flow resistance, high-resolution topography from close-range photogrammetry applied to rill erosion and the availability of published data from literature on step-pool streams. At first, the integration of a power velocity distribution allowed to obtain a theoretically-based expression of Darcy-Weisbach friction factor, in which Γ function and δ exponent of the velocity profile are included. Then this theoretically-deduced flow resistance relationship is calibrated and test…

Growth of stylolite teeth patterns depending on normal stress and finite compaction

2007

Abstract Stylolites are spectacular rough dissolution surfaces that are found in many rock types. They are formed during a slow irreversible deformation in sedimentary rocks and therefore participate to the dissipation of tectonic stresses in the Earth's upper crust. Despite many studies, their genesis is still debated, particularly the time scales of their formation and the relationship between this time and their morphology. We developed a new discrete simulation technique to explore the dynamic growth of the stylolite roughness, starting from an initially flat dissolution surface. We demonstrate that the typical steep stylolite teeth geometry can accurately be modelled and reproduce natu…

Melatonin in the seasonal response of the aphid Acyrthosiphon pisum.

2018

Aphids display life cycles largely determined by the photoperiod. During the warm long-day seasons, most aphid species reproduce by viviparous parthenogenesis. The shortening of the photoperiod in autumn induces a switch to sexual reproduction. Males and sexual females mate to produce overwintering resistant eggs. In addition to this full life cycle (holocycle), there are anholocyclic lineages that do not respond to changes in photoperiod and reproduce continuously by parthenogenesis. The molecular or hormonal events that trigger the seasonal response (i.e., induction of the sexual phenotypes) are still unknown. Although circadian synthesis of melatonin is known to play a key role in verteb…

In vivo photoprotection mechanisms observed from leaf spectral absorbance changes showing VIS–NIR slow-induced conformational pigment bed changes

2019

Abstract Regulated heat dissipation under excessive light comprises a complexity of mechanisms, whereby the supramolecular light-harvesting pigment–protein complex (LHC) shifts state from light harvesting towards heat dissipation, quenching the excess of photo-induced excitation energy in a non-photochemical way. Based on whole-leaf spectroscopy measuring upward and downward spectral radiance fluxes, we studied spectrally contiguous (hyperspectral) transient time series of absorbance A(λ,t) and passively induced chlorophyll fluorescence F(λ,t) dynamics of intact leaves in the visible and near-infrared wavelengths (VIS–NIR, 400–800 nm) after sudden strong natural-like illumination exposure. …

Multi-modal defences in aphids offer redundant protection and increased costs likely impeding a protective mutualism.

2017

The pea aphid, Acyrthosiphon pisum, maintains extreme variation in resistance to its most common parasitoid wasp enemy, Aphidius ervi, which is sourced from two known mechanisms: protective bacterial symbionts, most commonly Hamiltonella defensa, or endogenously encoded defences. We have recently found that individual aphids may employ each defence individually, occasionally both defences together, or neither. In field populations, Hamiltonella-infected aphids are found at low to moderate frequencies and while less is known about the frequency of resistant genotypes, they show up less often than susceptible genotypes in field collections. To better understand these patterns, we sought to co…

Absence inattendue d'espèces endémiques insulaires: Dissémination sur de longues distances chez des espèces de Siphonaria sub-antarctique de haute la…

2018

International audience; Aim: We assess biogeographical patterns, population structure and the range of species in the pulmonate genus Siphonaria across the sub‐Antarctic. We hypothesized that locally endemic cryptic species will be found across the distribution of these direct‐developing limpets in the sub‐Antarctic.Location: The sub‐Antarctic coasts of the Southern Ocean including South America, the Falkland/Malvinas, South Georgia, Kerguelen and Macquarie Islands.Methods: Multi‐locus phylogenetic reconstructions, mtDNA time‐calibrated divergence time estimations and population‐based analyses of Siphonaria populations were used at the scale of the Southern Ocean.Results: We resolve two wid…

2021

The scarcity of transcriptional regulatory genes in Buchnera aphidicola, an obligate endosymbiont in aphids, suggests the stability of expressed gene patterns and metabolic pathways. This observation argues in favor of the hypothesis that this endosymbiont bacteria might contribute little to the host adaptation when aphid hosts are facing challenging fluctuating environment. Finding evidence for the increased expression or silenced genes involved in metabolic pathways under the pressure of stress conditions and/or a given environment has been challenging for experimenters with this bacterial symbiotic model. Transcriptomic data have shown that Buchnera gene expression changes are confined t…

Immunity and other defenses in pea aphids, Acyrthosiphon pisum

2010

Background Recent genomic analyses of arthropod defense mechanisms suggest conservation of key elements underlying responses to pathogens, parasites and stresses. At the center of pathogen-induced immune responses are signaling pathways triggered by the recognition of fungal, bacterial and viral signatures. These pathways result in the production of response molecules, such as antimicrobial peptides and lysozymes, which degrade or destroy invaders. Using the recently sequenced genome of the pea aphid (Acyrthosiphon pisum), we conducted the first extensive annotation of the immune and stress gene repertoire of a hemipterous insect, which is phylogenetically distantly related to previously ch…