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(474) Production(s) de l'année 2018
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Consistency of modified gravity with a decreasing $G_{\rm eff}(z)$ in a $\Lambda$CDM background
Auteur(s): Gannouji Radouane, Kazantzidis Lavrentios, Perivolaropoulos Leandros, Polarski D.
(Article) Publié:
Physical Review D, vol. 98 p.104044 (2018)
Texte intégral en Openaccess :
Ref HAL: hal-01886014_v1
Ref Arxiv: 1809.07034
Ref INSPIRE: 1694683
DOI: 10.1103/PhysRevD.98.104044
WoS: 000451337400017
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
9 Citations
Résumé: Recent analyses [S. Nesseris et al., Phys. Rev. D 96, 023543 (2017)PRVDAQ2470-001010.1103/PhysRevD.96.023543; L. Kazantzidis and L. Pervolaropoulos, Phys. Rev. D 97, 103503 (2018)PRVDAQ2470-001010.1103/PhysRevD.97.103503] have indicated that an effective Newton’s constant Geff(z) decreasing with redshift may relieve the observed tension between the Planck15 best fit ΛCDM cosmological background (i.e., Planck15/ΛCDM) and the corresponding ΛCDM background favored by growth fσ8 and weak lensing data. We investigate the consistency of such a decreasing Geff(z) with some viable scalar-tensor models and f(R) theories. We stress that f(R) theories generically cannot lead to a decreasing Geff(z) for any cosmological background. For scalar-tensor models we deduce that in the context of a ΛCDM cosmological background, a decreasing Geff(z) is not consistent with a large Brans-Dicke parameter ωBD,0 today. This inconsistency remains and amplifies in the presence of a phantom dark energy equation of state parameter (w<-1). However, it can be avoided for w>-1. We also find that any modified gravity model with the required decreasing Geff(z) and Geff,0=G would have a characteristic signature in its growth index γ with 0.61≲γ0≲0.69 and large slopes γ0′, 0.16≲γ0′≲0.4, which is a characteristic signature of a decreasing (with z) Geff(z)
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Inducing and controlling rotation on small objects using photonic topological materials
Auteur(s): Frieder Lindel, Hanson George W., Antezza M., Buhmann Stefan Yoshi
(Article) Publié:
Physical Review B, vol. 98 p.144101 (2018)
Texte intégral en Openaccess :
Ref HAL: hal-01885407_v1
DOI: 10.1103/PhysRevB.98.144101
WoS: 000446135500002
Exporter : BibTex | endNote
3 Citations
Résumé: Photonic topological insulator plates violate Lorentz reciprocity, which leads to a directionality of surfaceguided modes. This in-plane directionality can be imprinted via an applied magnetic field. On the basis of macroscopic quantum electrodynamics in nonreciprocal media, we show that two photonic topological insulator surfaces are subject to a tunable, magnetic-field-dependent Casimir torque. Due to the directionality, this torque exhibits a unique 2π periodicity, in contradistinction to the Casimir torques encountered for reciprocal uniaxial birefringent media or corrugated surfaces which are π periodic. Remarkably, the torque direction and strength can be externally driven in situ by simply applying a magnetic field on the system, and we show that this can be exploited to induce a control of the rotation of small objects. Our predictions are relevant for nanooptomechanical experiments and devices.
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Ultrasensitive Displacement Noise Measurement of Carbon Nanotube Mechanical Resonators
Auteur(s): De bonis S. l., Urgell C., Yang W., Samanta C., Noury A., Vergara-cruz J., Dong Q., Jin Y., Bachtold A.
(Article) Publié:
Nano Letters, vol. 18 p.5324-5328 (2018)
Texte intégral en Openaccess :
Ref HAL: hal-01884447_v1
DOI: 10.1021/acs.nanolett.8b02437
WoS: WOS:000441478300097
Exporter : BibTex | endNote
16 Citations
Résumé: Mechanical resonators based on a singlecarbon nanotube are exceptional sensors of mass and force.The force sensitivity in these ultralight resonators is oftenlimited by the noise in the detection of the vibrations. Here,we report on an ultrasensitive scheme based on a RLCresonator and a low-temperature amplifier to detect nanotubevibrations. We also show a new fabrication process ofelectromechanical nanotube resonators to reduce the separation between the suspended nanotube and the gate electrodedown to ∼150 nm. These advances in detection and fabrication allow us to reach 0.5pm/ Hz displacement sensitivity.Thermal vibrations cooled cryogenically at 300 mK are detected with a signal-to-noise ratio as high as 17 dB. We demonstrate4.3zN/ Hz force sensitivity, which is the best force sensitivity achieved thus far with a mechanical resonator. Our work is animportant step toward imaging individual nuclear spins and studying the coupling between mechanical vibrations and electronsin different quantum electron transport regimes.
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Optical torque on a two-level system near a strongly nonreciprocal medium
Auteur(s): Hassani Gangaraj S. Ali, Silveirinha Mario, Hanson George W., Antezza M., Monticone Francesco
(Article) Publié:
Physical Review B, vol. 98 p.125146 (2018)
Texte intégral en Openaccess :
Ref HAL: hal-01883367_v1
DOI: 10.1103/PhysRevB.98.125146
WoS: 000445969100002
Exporter : BibTex | endNote
8 Citations
Résumé: We investigate the quantum optical torque on an atom interacting with an inhomogeneous electromagnetic environment described by the most general linear constitutive relations. The atom is modeled as a two-level system prepared in an arbitrary initial energy state. Using the Heisenberg equation of motion (HEM) and under the Markov approximation, we show that the optical torque has a resonant and nonresonant part, associated, respectively, with a spontaneous-emission process and Casimir-type interactions with the quantum vacuum, which can both be written explicitly in terms of the system Green function. Our formulation is valid for any three-dimensional inhomogeneous, dissipative, dispersive, nonreciprocal, and bianisotropic structure. We apply this general theory to a scenario in which the atom interacts with a material characterized by strong nonreciprocity and modal unidirectionality. In this case, the main decay channel of the atom energy is represented by the unidirectional surface waves launched at the nonreciprocal material-vacuum interface. To provide relevant physical insight into the role of these unidirectional surface waves in the emergence of nontrivial optical torque, we derive closed-form expressions for the induced torque under the quasistatic approximation. Finally, we investigate the equilibrium states of the atom polarization, along which the atom spontaneously tends to align due to the action of the torque. Our theoretical predictions may be experimentally tested with cold Rydberg atoms and superconducting qubits near a nonreciprocal material. We believe that our general theory may find broad application in the context of nanomechanical and biomechanical systems.
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Dynamics of the S(1D)+o-D2 --> SD+D reaction at low collision energies: revisiting the SH2 system
Auteur(s): Lara Manuel, Chefdeville Simon, Larregaray Pascal, Bonnet L., Launay Jean-Michel, Costes Michel, Naulin Christian, Jambrina Pablo G, Aoiz F Javier, Bergeat Astrid
(Affiches/Poster)
MOLEC 2018 (Dinard, FR), 2018-08-26
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Kinetic regimes in the curing process of epoxy-phenol composites
Auteur(s): Granado Lérys, Kempa Stefan, Gregoriades Laurence, Brüning Frank, Genix A.-C., Fréty Nicole, Anglaret E.
(Article) Publié:
Thermochimica Acta, vol. 667 p.185 - 192 (2018)
Ref HAL: hal-01881804_v1
DOI: 10.1016/j.tca.2018.07.019
WoS: 000444663600024
Exporter : BibTex | endNote
9 Citations
Résumé: Despite an abundant literature on epoxy-amine systems, a complete description of the curing kinetics in epoxy-phenol composites was still lacking. In this study, the curing kinetics of an epoxy-phenol composite relevant to microelectronics industry is probed by isothermal and non-isothermal differential scanning calorimetry. An isoconversional analysis of the data reveals a significant contribution of the diffusion of molecular species to the activation energy, at low temperature and high degrees of curing. A model-fitting of the kinetics is performed in two successive steps: high-temperatures data are fitted with Arrhenius law and nth order autocatalytic model (where the diffusion contribution is neglected), whereas low-temperature data are fitted using Rabinowitch and modified-Williams-Landel-Ferry models (considering a diffusion contribution related to the glass transition). The chemical and diffusion contributions to the rate constants are calculated at various temperatures, clarifying the kinetics regimes with precision. Finally, the kinetics regimes are summarized in an improved time-temperature-transformation diagram.
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Surfing on protein waves: proteophoresis as a mechanism for bacterial genome partitioning
Auteur(s): Walter J.-C.
Conference: Biophychrom18: The Biology and Physics of Bacterial Chromosome Organisation (Leiden, NL, 2018-06-04)
Texte intégral en Openaccess :
Ref HAL: hal-01881168_v1
Exporter : BibTex | endNote
Résumé: Efficient bacterial chromosome segregation typically requires the coordinated action of a three-component, fueled by adenosine triphosphate machinery called the partition complex. We present a phenomenological model accounting for the dynamic activity of this system that is also relevant for the physics of catalytic particles in active environments. The model is obtained by coupling simple linear reaction-diffusion equations with a proteophoresis, or “volumetric” chemophoresis, force field that arises from protein-protein interactions and provides a physically viable mechanism for complex translocation. This minimal description captures most known experimental observations: dynamic oscillations of complex components, complex separation and subsequent symmetrical positioning. The predictions of our model are in phenomenological agreement with and provide substantial insight into recent experiments. From a non-linear physics view point, this system explores the active separation of matter at micrometric scales with a dynamical instability between static positioning and travelling wave regimes triggered by the dynamical spontaneous breaking of rotational symmetry.
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