Carbon epoxy composites thermal conductivity at 80 K and 300 K

The in-plane and in-depth thermal conductivities of epoxy-carbon fiber composites have been measured at 77 K and 300 K. The experimental technique rests on the hot disk method. The two thermal conductivities as well as the thermal contact resistance between the probe and the composite materials are estimated from measurement data and an analytical heat transfer model within the experimental configuration. The results obtained at 77 K explained well the ignition test results performed on the composites at 77 K with regards to liquid oxygen storage

Caractérisation thermique des matériaux pour mémoires à changement de phase à haute température et échelle submicrométrique.

Les PCM (Phase Change Memory) développés par l’industrie microélectronique utilisent des verres chalcogénures des systèmes Ge-Sb-Te pour assurer le stockage de données informatiques par changement de structures cristallines. Le principe de stockage de l'information repose sur la différence de résistivité électrique entre l’état amorphe et l’état cristallin de ces verres, le passage entre ces différents états s’effectuant par chauffage (effet Joule). Il est fondamental, afin de maîtriser ces phénomènes de changement de phase pour le stockage des données, de connaître les propriétés thermiques de ces matériaux. On mesure ainsi la conductivité thermique de couche mince de faible épaisseur (100 nm – 800 nm) sur une plage de température de 25°C à 400°C. La résistance d’interface entre le GST et le diélectrique utilisé dans les PCM (ici du SiO2) est aussi estimée

Effect of characteristic size on the collective phonon transport in crystalline GeTe

We study the effect of characteristic size variation on the phonon thermal transport in crystalline GeTe for a wide range of temperatures using the first-principles density-functional method coupled with the kinetic collective model approach. The characteristic size dependence of phonon thermal transport reveals an intriguing collective phonon transport regime, located in between the ballistic and the diffusive transport regimes. Therefore, systematic investigations have been carried out to describe the signatures of phonon hydrodynamics via the competitive effects between grain size and temperature. A characteristic nonlocal length associated with phonon hydrodynamics and a heat wave propagation length has been extracted. The connections between phonon hydrodynamics and these length scales are discussed in terms of the Knudsen number. Further, the scaling relation of thermal conductivity as a function of characteristic size in the intermediate size range emerges as a crucial indicator of the strength of the hydrodynamic behavior. A ratio concerning normal and resistive scattering rates has been employed to understand these different scaling relations, which seems to control the strength and prominent visibility of the collective phonon transport in GeTe. This systematic investigation emphasizes the importance of the competitive effects between temperature and characteristic size on phonon hydrodynamics in GeTe, which can lead to a better understanding of the generic behavior and consequences of the phonon hydrodynamics and its controlling parameters in low-thermal conductivity materials

The use of photothermal techniques for thermal conductivity and thermal boundary resistance measurements of phase-change chalcogenides alloys

This article presents three photothermal methods dedicated to the measurement of the thermal properties of chalcogenide alloys, used as a central element in the new generations of non-volatile memory. These materials have two phases, amorphous and crystalline, possessing a sharp contrast in their electrical and thermal properties. In the crystalline phase, the properties also change very significantly with temperature. The control of the temperature of the samples, the choice of transducers, and the time or frequency characteristic values of the photothermal excitation are thoroughly discussed. Each photothermal technique is described from the experimental point of view as well as from the inverse method, performed to identify the parameters of interest. The identified thermal properties mainly concern the thermal conductivity and the thermal resistance at the interfaces between the phase-change materials and the materials in contact as encountered in the production of the microelectronic memory device. Assessing various photothermal techniques, the study suggests that pulsed photothermal radiometry is the most effective method for sensitive high-temperature measurements of thermal properties of the phase-change materials

Significant four-phonon scattering and its heat transfer implications in crystalline Ge2Sb2Te5

We systematically demonstrate the temperature-dependent thermal transport properties in crystalline Ge2Sb2Te5 via first-principles density functional theory informed linearized Boltzmann transport equation. The investigation, covering a wide temperature range (30–600 K), reports the emergence of an unusual optical-phonon-dominated thermal transport in crystalline Ge2Sb2Te5. Further, a significant contribution of four-phonon scattering is recorded which markedly alters the lattice thermal conductivity. Therefore, the combined effect of cubic and quartic phonon anharmonicity is seen to navigate the underlying physical mechanism and open up intriguing phononic interactions in Ge2Sb2Te5 at high temperature. Irrespective of three- and four-phonon processes, umklapp is seen to prevail over normal scattering events. Consequently, four-phonon scattering is found to notably reduce the lattice thermal conductivity of Ge2Sb2Te5 to 28% at room temperature and 42% at higher temperature. This quartic anharmonicity further manifests in the breakdown of T−1 scaling of thermal conductivity and challenges the idea of a universal lower bound to phononic thermal diffusivity at high temperature. The faster decay of thermal diffusivity compared to T−1 is rationalized encompassing the quartic anharmonicity via a modified timescale. These results invoke better understanding and precision to the theoretical prediction of thermal transport properties of Ge2Sb2Te5. Concomitantly, this also triggers the possibility to explore the manifestations of the lower bound of thermal diffusivity in materials possessing pronounced four-phonon scattering

Vitamin B12-Impaired Metabolism Produces Apoptosis and Parkinson Phenotype in Rats Expressing the Transcobalamin-Oleosin Chimera in Substantia Nigra

International audienceThe development of fearfulness and the capacity of animals to cope with stressful events are particularly sensitive to early experience with mothers in a wide range of species. However, intrinsic characteristics of young animals can modulate maternal influence. This study evaluated the effect of intrinsic fearfulness on non-genetic maternal influence. Quail chicks, divergently selected for either higher (LTI) or lower fearfulness (STI) and from a control line (C), were cross-fostered by LTI or STI mothers. Behavioural tests estimated the chicks' emotional profiles after separation from the mother. Whatever their genotype, the fearfulness of chicks adopted by LTI mothers was higher than that of chicks adopted by STI mothers. However, genetic background affected the strength of maternal effects: the least emotional chicks (STI) were the least affected by early experience with mothers. We demonstrated that young animal's intrinsic fearfulness affects strongly their sensitivity to non-genetic maternal influences. A young animal's behavioural characteristics play a fundamental role in its own behavioural development processes

The periodic pulse photothermal radiometry technique within the front face configuration

The front face photothermal radiometry technique has been improved in order to estimate the thermal conductivity of thin films with better accuracy compared to existing techniques. The experimental pro- cedure is based on the front face response to a nanoseconds laser pulse repeated periodically at high fre- quency, i. e., a Dirac comb waveform. Averaging the thermal response by considering thousands successive pulses allows improving largely the signal noise ratio. The unknown thermal properties and related experimental parameters are identified by minimizing the gap between the measured signal and the theoretical response that accounts with the pulse waveform, the repetition frequency and the detector transfer function. Minimization is first achieved by implementing first a simplex technique that gives an initial set of values to start the Metropolis–Hastings algorithm in a second step. Application of the proposed methodology is done considering amorphous GeTe film deposited on a Si wafer. It is shown that this experimental method as well as the implementation of the Bayes minimization technique allows to identify the thin film intrinsic thermal conductivity with high accuracy considering some uncertainty on the other parameters assumed to be known

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements