855 research outputs found
Le balnéaire De la Manche au monde
Ce livre offre un regard renouvelĂ© sur le phĂ©nomĂšne balnĂ©aire pour mieux comprendre comment le littoral a Ă©tĂ© investi depuis plus de deux siĂšcles par de nouvelles pratiques dĂ©veloppant un « habiter » original des bords de mer. Ce modĂšle du XIXe siĂšcle sâest pĂ©rennisĂ©, diffusĂ©, modifiĂ© pour conquĂ©rir progressivement mais inexorablement la planĂšte entiĂšre. Câest cette circulation dâun modĂšle architectural, patrimonial, culturel, Ă©conomique et social qui est abordĂ©e et analysĂ©e au fil des pages et des illustrations
Phosphate availability and the ultimate control of new nitrogen input by nitrogen fixation in the tropical Pacific Ocean
International audienceDue to the low atmospheric input of phosphate into the open ocean, it is one of the key nutrients that could ultimately control primary production and carbon export into the deep ocean. The observed trend over the last 20 years has shown a decrease in the dissolved inorganic phosphate (DIP) pool in the North Pacific gyre, which has been correlated to the increase in di-nitrogen (N2) fixation rates. Following a NW-SE transect, in the Southeast Pacific during the early austral summer (BIOSOPE cruise), we present data on DIP, dissolved organic phosphate (DOP) and particulate phosphate (PP) pools along with DIP turnover times (TDIP) and N2 fixation rates. We observed a decrease in DIP concentration from the edges to the centre of the gyre. Nevertheless the DIP concentrations remained above 100 nmol L-1 and T DIP was more than 6 months in the centre of the gyre; DIP availability remained largely above the level required for phosphate limitation to occur and the absence of Trichodesmium spp and low nitrogen fixation rates were likely to be controlled by other factors such as temperature or iron availability. This contrasts with recent observations in the North Pacific Ocean at the ALOHA station and in the western Pacific Ocean at the same latitude (DIAPALIS cruises) where lower DIP concentrations (-1) and T DIP 2 fixation rates and possibly carbon dioxide sequestration, if the primary ecophysiological controls, temperature and/or iron availability, were alleviated
Effect of chromophore-chromophore electrostatic interactions in the NLO response of functionalized organic-inorganic sol-gel materials
In the last years, important non-linear optical results on sol-gel and
polymeric materials have been reported, with values comparable to those found
in crystals. These new materials contain push-pull chromophores either
incorporated as guest in a high Tg polymeric matrix (doped polymers) or grafted
onto the polymeric matrix. These systems present several advantages; however
they require significant improvement at the molecular level - by designing
optimized chromophores with very large molecular figure of merit, specific to
each application targeted. Besides, it was recently stated in polymers that the
chromophore-chromophore electrostatic interactions, which are dependent of
chromophore concentration, have a strong effect into their non-linear optical
properties. This has not been explored at all in sol-gel systems. In this work,
the sol-gel route was used to prepare hybrid organic-inorganic thin films with
different NLO chromophores grafted into the skeleton matrix. Combining a
molecular engineering strategy for getting a larger molecular figure of merit
and by controlling the intermolecular dipole-dipole interactions through both:
the tuning of the push-pull chromophore concentration and the control of TEOS
(Tetraethoxysilane) concentration, we have obtained a r33 coefficient around 15
pm/V at 633 nm for the classical DR1 azo-chromophore and a r33 around 50 pm/V
at 831 nm for a new optimized chromophore structure.Comment: 10 pages, 11 figures, 1 tabl
ââCooling by Heatingââ- Demonstrating the Significance of the Longitudinal Specific Heat
Heating a solid sphere at its surface induces mechanical stresses inside the sphere. If a finite amount of heat is supplied, the stresses gradually disappear as temperature becomes homogeneous throughout the sphere. We show that before this happens, there is a temporary lowering of pressure and density in the interior of the sphere, inducing a transient lowering of the temperature here. For ordinary solids this effect is small because c_{p}â
c_{V}. For fluent liquids the effect is negligible because their dynamic shear modulus vanishes. For a liquid at its glass transition, however, the effect is generally considerably larger than in solids. This paper presents analytical solutions of the relevant coupled thermoviscoelastic equations. In general, there is a difference between the isobaric specific heat c_{p} measured at constant isotropic pressure and the longitudinal specific heat c_{l} pertaining to mechanical boundary conditions that confine the associated expansion to be longitudinal. In the exact treatment of heat propagation, the heat-diffusion constant contains c_{l} rather than c_{p}. We show that the key parameter controlling the magnitude of the âcooling-by-heatingâ effect is the relative difference between these two specific heats. For a typical glass-forming liquid, when the temperature at the surface is increased by 1Â K, a lowering of the temperature at the sphere center of the order of 5Â mK is expected if the experiment is performed at the glass transition. The cooling-by-heating effect is confirmed by measurements on a glucose sphere at the glass transition
Illusory perceptions of space and time preserve cross-saccadic perceptual continuity
When voluntary saccadic eye movements are made to a silently ticking clock, observers sometimes think that the second hand takes longer than normal to move to its next position. For a short period, the clock appears to have stopped (chronostasis). Here we show that the illusion occurs because the brain extends the percept of the saccadic target backwards in time to just before the onset of the saccade. This occurs every time we move the eyes but it is only perceived when an external time reference alerts us to the phenomenon. The illusion does not seem to depend on the shift of spatial attention that accompanies the saccade. However, if the target is moved unpredictably during the saccade, breaking perception of the target's spatial continuity, then the illusion disappears. We suggest that temporal extension of the target's percept is one of the mechanisms that 'fill in' the perceptual 'gap' during saccadic suppression. The effect is critically linked to perceptual mechanisms that identify a target's spatial stability
Influence of hand position on the near-effect in 3D attention
Voluntary reorienting of attention in real depth situations is characterized by an attentional bias to locations near the viewer once attention is deployed to a spatially cued object in depth. Previously this effect (initially referred to as the ânear-effectâ) was attributed to access of a 3D viewer-centred spatial representation for guiding attention in 3D space. The aim of this study was to investigate whether the near-bias could have been associated with the position of the response-hand, always near the viewer in previous studies investigating endogenous attentional shifts in real depth. In Experiment 1, the response-hand was placed at either the near or far target depth in a depth cueing task. Placing the response-hand at the far target depth abolished the near-effect, but failed to bias spatial attention to the far location. Experiment 2 showed that the response-hand effect was not modulated by the presence of an additional passive hand, whereas Experiment 3 confirmed that attentional prioritization of the passive hand was not masked by the influence of the responding hand on spatial attention in Experiment 2. The pattern of results is most consistent with the idea that response preparation can modulate spatial attention within a 3D viewer-centred spatial representation
A Laboratory Study of the Effects of Size, Density, and Shape on the WaveâInduced Transport of Floating Marine Litter
Floating marine litter is transported by several mechanisms, including surface waves. In studies of marine litter transport, the waveâinduced drift is set to be equal to the Stokes drift, corresponding to the Lagrangianâmean waveâinduced drift of an infinitesimally small tracer. Largeâscale experiments are used to show how the waveâinduced drift of objects of finite size depends on their size, density, and shape. We observe increases in drift of 95% compared to Stokes drift for discs with diameters of 13% of the wavelength, up to 23% for spheres with diameters of 3% of the wavelength, whereas drift is reduced for objects that become submerged such as nets. We investigate what these findings may imply for the transport of plastic pollution in realistic wave conditions and we predict an increase in waveâinduced drift for (very) large plastic pollution objects. The different extrapolation techniques we explore to make this prediction exhibit a large range of uncertainty
Response of CsI(Tl) scintillators over a large range in energy and atomic number of ions (Part I): recombination and delta -- electrons
A simple formalism describing the light response of CsI(Tl) to heavy ions,
which quantifies the luminescence and the quenching in terms of the competition
between radiative transitions following the carrier trapping at the Tl
activator sites and the electron-hole recombination, is proposed. The effect of
the delta rays on the scintillation efficiency is for the first time
quantitatively included in a fully consistent way. The light output expression
depends on four parameters determined by a procedure of global fit to
experimental data.Comment: 28 pages, 6 figures, submitted to Nucl. Inst. Meth.
Recommended from our members
Biases in the perceived timing of perisaccadic perceptual and motor events
Subjects typically experience the temporal interval immediately following a saccade as longer than a comparable control interval. One explanation of this effect is that the brain antedates the perceptual onset of a saccade target to around the time of saccade initiation. This could explain the apparent continuity of visual perception across eye movements. Thisantedating account was tested in three experiments in which subjects made saccades of differing extents and then judged either the duration or the temporal order of key events. Postsaccadic stimuli underwent subjective temporal lengthening and had early perceived onsets. A temporally advanced awareness of saccade completion was also found, independently of antedating effects. These results provide convergent evidence supporting antedating and differentiating it from other temporal biases
- âŠ