Two-dimensional shear modulus of a Langmuir foam

We deform a two-dimensional (2D) foam, created in a Langmuir monolayer, by applying a mechanical perturbation, and simultaneously image it by Brewster angle microscopy. We determine the foam stress tensor (through a determination of the 2D gas-liquid line tension, 2.35 $\pm$ 0.4 pJ$\cdot$m$^{-1}$) and the statistical strain tensor, by analyzing the images of the deformed structure. We deduce the 2D shear modulus of the foam, $\mu= 38 \pm 3 \mathrm{nN}\cdot \mathrm{m}^{-1}$. The foam effective rigidity is predicted to be $35 \pm 3 \mathrm {nN}\cdot \mathrm {m}^{- 1}$, which agrees with the value $37.5 \pm 0.8 \mathrm {nN}\cdot \mathrm {m}^{-1}$ obtained in an independent mechanical measurement.Comment: submitted May 12, 2003 ; resubmitted Sept 9, 200

Quantum fluctuations for drag free geodesic motion

The drag free technique is used to force a proof mass to follow a geodesic motion. The mass is protected from perturbations by a cage, and the motion of the latter is actively controlled to follow the motion of the proof mass. We present a theoretical analysis of the effects of quantum fluctuations for this technique. We show that a perfect drag free operation is in principle possible at the quantum level, in spite of the back action exerted on the mass by the position sensor.Comment: 4 pages, 1 figure, RevTeX, minor change

Chirality transfer and stereo-selectivity of imprinted cholesteric networks

Imprinting of cholesteric textures in a polymer network is a method of preserving a macroscopically chiral phase in a system with no molecular chirality. By modifying the elastics properties of the network, the resulting stored helical twist can be manipulated within a wide range since the imprinting efficiency depends on the balance between the elastics constants and twisting power at network formation. One spectacular property of phase chirality imprinting is the created ability of the network to adsorb preferentially one stereo-component from a racemic mixture. In this paper we explore this property of chirality transfer from a macroscopic to the molecular scale. In particular, we focus on the competition between the phase chirality and the local nematic order. We demonstrate that it is possible to control the subsequent release of chiral solvent component from the imprinting network and the reversibility of the stereo-selective swelling by racemic solvents

Stereo-selective swelling of imprinted cholesteric networks

Molecular chirality, and the chiral symmetry breaking of resulting macroscopic phases, can be topologically imprinted and manipulated by crosslinking and swelling of polymer networks. We present a new experimental approach to stereo-specific separation of chiral isomers by using a cholesteric elastomer in which a helical director distribution has been topological imprinted by crosslinking. This makes the material unusual in that is has a strong phase chirality, but no molecular chirality at all; we study the nature and parameters controlling the twist-untwist transition. Adding a racemic mixture to the imprinted network results in selective swelling by only the component of ``correct'' handedness. We investigate the capacity of demixing in a racemic environment, which depends on network parameters and the underlying nematic order

Quantum noise in ideal operational amplifiers

We consider a model of quantum measurement built on an ideal operational amplifier operating in the limit of infinite gain, infinite input impedance and null output impedance and with a feddback loop. We evaluate the intensity and voltage noises which have to be added to the classical amplification equations in order to fulfill the requirements of quantum mechanics. We give a description of this measurement device as a quantum network scattering quantum fluctuations from input to output ports.Comment: 4 pages, 2 figures, RevTe

Mid‐Holocene site formation, diagenesis and human activity at the foothills of Serra da Estrela (Portugal)

UIDB/00749/2020 UIDP/00749/2020The Neolithic occupation of Penedo dos Mouros in the foothills of Serra da Estrela, Portugalʼs highest mountain, dates to the 5th to 4th millennia cal B.C. The siteʼs faunal assemblage is extremely rare in the regional prehistoric archaeological record, due to the acidity of the granitic geology. This underlines Penedo dos Mouros importance as a reference site for understanding early pastoralism in the region. Due to the insufficient survival of bone collagen for radiocarbon dating and the homogeneity of the stratigraphy, where most visible contacts are due to postdepositional processes, we chose micromorphology to address the reasons behind the bone preservation and to assess the stratigraphic integrity of the prehistoric deposit. Reworking of eroding saprolitic soils was a major factor in the sediment accumulation, with remains of short human occupation events. Possible evidence for clearance fires linked to the first occurrences of pastoralism practised in the region, creating open spaces for grazing, was identified. Post‐depositional carbonate cementation derived from ashes, identifiable at the microscopic scale, enabled bone preservation. Carbonate and spodic‐like features document water saturation once the sedimentation ceased. This sedimentary dynamic has broader geomorphological implications, such as an inferred post‐Neolithic incision of the stream valley adjacent to the site.publishersversionpublishe

Radioscience simulations in General Relativity and in alternative theories of gravity

In this communication, we focus on the possibility to test GR with radioscience experiments. We present a new software that in a first step simulates the Range/Doppler signals directly from the space time metric (thus in GR and in alternative theories of gravity). In a second step, a least-squares fit of the involved parameters is performed in GR. This software allows one to get the order of magnitude and the signature of the modifications induced by an alternative theory of gravity on radioscience signals. As examples, we present some simulations for the Cassini mission in Post-Einsteinian gravity and with the MOND External Field Effect.Comment: 4 pages; Proceedings of "Les Rencontres de Moriond 2011 - Gravitation session

Disc heating: comparing the Milky Way with cosmological simulations

We present an analysis of a suite of simulations run with different particle- and grid-based cosmological hydrodynamical codes and compare them with observational data of the Milky Way. This is the first study to make comparisons of properties of galaxies simulated with particle- and grid-based codes. Our analysis indicates that there is broad agreement between these different modelling techniques. We study the velocity dispersion-age relation for disc stars at z= 0 and find that four of the simulations are more consistent with observations by Holmberg, Nordstroem & Andersen in which the stellar disc appears to undergo continual/secular heating. Two other simulations are in better agreement with the Quillen & Garnett observations that suggest ‘saturation' in the heating profile for young stars in the disc. None of the simulations has thin discs as old as that of the Milky Way. We also analyse the kinematics of disc stars at the time of their birth for different epochs in the galaxies' evolution and find that in some simulations old stars are born cold within the disc and are subsequently heated, while other simulations possess old stellar populations which are born relatively hot. The models which are in better agreement with observations of the Milky Way's stellar disc undergo significantly lower minor-merger/assembly activity after the last major merger, that is, once the disc has formed. All of the simulations are significantly ‘hotter' than the Milky Way disc; on top of the effects of mergers, we find a ‘floor' in the dispersion that is related to the underlying treatment of the heating and cooling of the interstellar medium, and the low density threshold which such codes use for star formation. This finding has important implications for all studies of disc heating that use hydrodynamical code