1,391 research outputs found
Non equilibrium thermodynamics and cosmological pancakes formation
We investigate the influence of non equilibrium thermodynamics on
cosmological structure formation. In this paper, we consider the collapse of
planar perturbations usually called "Zel'dovich pancakes". We have developed
for that purpose a new two fluids (gas and dark matter) hydrodynamical code,
with three different thermodynamical species: electrons, ions and neutral
particles (T_e\ne T_i \ne T_n). We describe in details the complex structure of
accretion shock waves. We include several relevant processes for a low density,
high temperature, collisional plasma such as non-equilibrium chemical
reactions, cooling, shock heating, thermal energy equipartition between
electrons, ions and neutral particles and electronic conduction. We find two
different regions in the pancake structure: a thermal precursor ahead of the
compression front and an equipartition wave after the compression front where
electrons and ions temperatures differ significantly. This complex structure
may have two interesting consequences: pre-heating of unshocked regions in the
vicinity of massive X-ray clusters and ions and electrons temperatures
differences in the outer regions of X-rays clusters.Comment: 30 pages, including 8 figures, accepted for publication in The
Astrophysical Journa
Rotational intermittency and turbulence induced lift experienced by large particles in a turbulent flow
The motion of a large, neutrally buoyant, particle, freely advected by a
turbulent flow is determined experimentally. We demonstrate that both the
translational and angular accelerations exhibit very wide probability
distributions, a manifestation of intermittency. The orientation of the angular
velocity with respect to the trajectory, as well as the translational
acceleration conditioned on the spinning velocity provide evidence of a lift
force acting on the particle.Comment: 4 page, 4 figure
Allelopathy Effect of the Blue Diatom HasleaOstrearia (Gaillon) Simonsen: Growth Inhibition in Aquaculture Relevant Microalgae
We are well known that the marine pennate diatom Hasleaostrearia (Gaillon) Simonsen produces the blue-green pigment called marennine. Marennine was identified as a polyphenolic compound. This compound is capable to inhibit the growth of herpes simplex virus type 1 (HSV-1) and several bacteria, including pathogens as Vibrio sp. The aim of this study was to determine how strong the allelophatic effect of marennine is generated byH. ostrearia and identifying its minimal concentration that inhibits the growth of other microalgae. The experiment consisted of two phases of research activities. The first phase was biovolumecomparaison between H. ostrearia and microalgae suitable for aquaculture tested to take into account the differences in size of the microalgae tested(Tetraselmissuecica, Chaetocerosgracilis, Skeletonemacostatum, PavlovalutheriandIsochrysisgalbana (T-Iso) in term of H. ostrearia biomass and production of marennine. The second phase was the bioactivity tests, which is include growth kinetics, allelophatic effects and concentration of marennine in the culture medium, measured with spectrophotometer. The results of this study showed that H. ostrearia could inhibit several species of microalgae currently used in aquaculture (T. suecica, C. gracilis and S. costatum). The statistical analysis (One way ANOVA) showed that there are significant differences (P < 0, 05) between treatments andwhen co-cultured with H. ostrearia, these microalgae exhibited a significant growth inhibition. The highest inhibition value was 97.77% (on the treatementH. ostrearia+C. gracilis). In this treatment, the concentration of marennine in the culture was 5.35 mg L-1. According to the results, we can conclude that the supernatant of H. ostrearia with marennine acts as an allelochemical. The minimal concentration is 0.23 mg L-1 and the highest is 5.35 mg L-1. The treatments H. ostreariawithP. lutheri and T-Iso did not performed any inhibition
Detection of Helium in the Atmosphere of the Exo-Neptune HAT-P-11b
The helium absorption triplet at a wavelength of 10,833 \AA\ has been
proposed as a way to probe the escaping atmospheres of exoplanets. Recently
this feature was detected for the first time using Hubble Space Telescope (HST)
WFC3 observations of the hot Jupiter WASP-107b. We use similar HST/WFC3
observations to detect helium in the atmosphere of the hot Neptune HAT-P-11b at
the confidence level. We compare our observations to a grid of 1D
models of hydrodynamic escape to constrain the thermospheric temperatures and
mass loss rate. We find that our data are best fit by models with high mass
loss rates of - g s. Although we do
not detect the planetary wind directly, our data are consistent with the
prediction that HAT-P-11b is experiencing hydrodynamic atmospheric escape.
Nevertheless, the mass loss rate is low enough that the planet has only lost up
to a few percent of its mass over its history, leaving its bulk composition
largely unaffected. This matches the expectation from population statistics,
which indicate that close-in planets with radii greater than 2 R
form and retain H/He-dominated atmospheres. We also confirm the independent
detection of helium in HAT-P-11b obtained with the CARMENES instrument, making
this the first exoplanet with the detection of the same signature of
photoevaporation from both ground- and space-based facilities.Comment: 12 pages, 9 figures, accepted for publication in ApJ
Optical characterization of a SCISSOR device.
Here, we report on the design, fabrication and characterization of single-channel (SC-) and dual-channel (DC-) side-coupled integrated spaced sequences of optical resonators (SCISSOR) with a finite number (eight) of microring resonators using submicron silicon photonic wires on a silicon-on-insulator (SOI) wafer. We present results on the observation of multiple resonances in the through and the drop port signals of DC-SCISSOR. These result from the coupled resonator induced transparency (CRIT) which appears when the resonator band (RB) and the Bragg band (BB) are nearly coincident. We also observe the formation of high-Q (> 23000) quasi-localized modes in the RB of the drop transmission which appear when the RB and BB are well separated from each other. These multiple resonances and quasi-localized modes are induced by nanometer-scale structural disorders in the dimension of one or more rings. Finally, we demonstrate the tunability of RB (and BB) and localized modes in the DC-SCISSOR by thermo-optical or free-carrier refraction
Characterizing flows with an instrumented particle measuring Lagrangian accelerations
We present in this article a novel Lagrangian measurement technique: an
instrumented particle which continuously transmits the force/acceleration
acting on it as it is advected in a flow. We develop signal processing methods
to extract information on the flow from the acceleration signal transmitted by
the particle. Notably, we are able to characterize the force acting on the
particle and to identify the presence of a permanent large-scale vortex
structure. Our technique provides a fast, robust and efficient tool to
characterize flows, and it is particularly suited to obtain Lagrangian
statistics along long trajectories or in cases where optical measurement
techniques are not or hardly applicable.Comment: submitted to New Journal of Physic
Individual and collective stock dynamics: intra-day seasonalities
We establish several new stylised facts concerning the intra-day
seasonalities of stock dynamics. Beyond the well known U-shaped pattern of the
volatility, we find that the average correlation between stocks increases
throughout the day, leading to a smaller relative dispersion between stocks.
Somewhat paradoxically, the kurtosis (a measure of volatility surprises)
reaches a minimum at the open of the market, when the volatility is at its
peak. We confirm that the dispersion kurtosis is a markedly decreasing function
of the index return. This means that during large market swings, the
idiosyncratic component of the stock dynamics becomes sub-dominant. In a
nutshell, early hours of trading are dominated by idiosyncratic or sector
specific effects with little surprises, whereas the influence of the market
factor increases throughout the day, and surprises become more frequent.Comment: 9 pages, 7 figure
Directional silicon nano-antennas for quantum emitter control designed by evolutionary optimization
We optimize silicon nano-antennas to enhance and steer the emission of local
quantum sources. We combine global evolutionary optimization (EO) with
frequency domain electrodynamical simulations, and compare design strategies
based on resonant and non-resonant building blocks. Specifically, we
investigate the performance of models with different degrees of freedom but
comparable amount of available material. We find that simpler geometric models
allow significantly faster convergence of the optimizer, which, expectedly,
comes at the cost of a reduced optical performance. We finally analyze the
physical mechanisms underlying the directional emission that also comes with an
emission rate enhancement, and find a surprising robustness against
perturbations of the source emitter location. This makes the structures highly
interesting for actual nano-fabrication. We believe that optimized,
all-dielectric silicon nano-antennas have high potential for genuine
breakthroughs in a multitude of applications in nanophotonics and quantum
technologies.Comment: 8 pages, 6 figure
Different distribution of malaria parasite in left and right extremities of vertebrate hosts translates into differences in parasite transmission
International audienceMalaria, a vector-borne disease caused by Plasmodium spp., remains a major global cause of mortality. Optimization of disease control strategies requires a thorough understanding of the processes underlying parasite transmission. While the number of transmissible stages (gametocytes) of Plasmodium in blood is frequently used as an indicator of host-to-mosquito transmission potential, this relationship is not always clear. Significant effort has been made in developing molecular tools that improve gametocyte density estimation and therefore prediction of mosquito infection rates. However a significant level of uncertainty around estimates remains. The weakness in the relationship between gametocyte burden, measured from a blood sample, and the mosquito infection rate could be explained by a non-homogeneous distribution of gametocytes in the bloodstream. The estimated gametocyte density would then only be a single snapshot that does not reflect the host infectivity. This aspect of Plasmodium infection, however, remains largely neglected. In both humans and birds, we found here that the gametocyte densities differed depending on which side of the body the sample was taken, suggesting that gametocytes are not homogeneously distributed within the vertebrate host. We observed a fluctuating asymmetry, in other words, the extremity of the body with the highest density of parasites is not always the same from one individual to another. An estimation of gametocyte density from only one blood sample, as is commonly measured, could, therefore, over-or underestimated the infectivity of gametocyte carriers. This might have important consequences on the epidemiology of the disease since we show that this variation influences host-to-mosquito transmission. Vectors fed on the least infected body part had a lower parasite burden than those fed on the most infected part. The heterogeneous distribution of gametocytes in bloodstream should be considered to improve diagnosis and test new malaria control strategies
Metal-mediated linear self-assembly of porphyrins
Porphyrin derivatives are highly relevant to biological processes such as light harvesting and charge separation. Their aromatic electronic structure and their accessible HOMO−LUMO gap render porphyrins highly attractive for the development of opto- and electro-active materials. Due to the often difficult covalent synthesis of multiporphyrins, self-assembly using metal complexation as the driving force can lead to well defined objects exhibiting a controlled morphology, which will be required to analyse and understand the electronic properties of porphyrin wires. This article presents two assembly approaches, namely by peripheral coordination or by binding to a metal ion in the porphyrin core, that are efficient and well designed for future developments requiring interactions with a surface
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