Effects of Ag or Si on precipitation in the alloy Al-2.5% Cu-1.5% Mg

International audienceCalorimetric measurements and electron microscopy observations were performed on Al-2.5 mass% Cu-1.5 mass% Mg alloys containing also 0.4, 1 or 2 % Ag or 0.5 % Si, in order to improve understanding of the relationships between precipitation processes and age hardening. The analogous behaviour of calorimetric and hardness data confirms that the first hardening stage is initiated in all alloys by GPB zone formation which occurs via a nucleation and growth controlled mechanism. The vacancy-trapping effect of Mg is increased by Ag and Si additions and leads to slower precipitation kinetics. Consequently refined GPB zones sizes are obtained leading to an increase in hardness with respect to the ternary alloy. During the second hardening stage, the formation of the more stable S' phase increases the total amount of strengthening precipitates in the ternary alloy. Phases typical for binary Al-Cu alloys form additionally in the Si-containing alloy. In the Ag-bearing alloys, precipitation of the hardening X' phase occurs the earlier the higher the Ag content is; it is followed by S' precipitation. During heating of the ternary alloy, the S'phase forms after substantial dissolution of GPB zones and of the S" phase identified by high resolution electron microscopy; this contradicts the concept of a continuous precipitation sequence

Metrics for the violation of detailed balance in microwave circuits: theory and experiment

We propose a new approach to detailed balance violation in electrical circuits by relying on the scattering matrix formalism commonly used in microwave electronics. This allows to include retardation effects which are paramount at high frequencies. We define the spectral densities of phase space angular momentum, heat transfer and cross power, which can serve as criteria for detailed balance violation. We confirm our theory with measurements in the 4-8 GHz frequency range on several two port circuits of varying symmetries, in space and time. This validates our approach, which will allow to treat quantum circuits at ultra-low temperature

Soil to Sail - Asteroid Landers on Near-Term Sailcraft as an Evolution of the GOSSAMER Small Spacecraft Solar Sail Concept for In-Situ Characterization

Any effort which intends to physically interact with specific asteroids requires understanding at least of the composition and multi-scale structure of the surface layers, sometimes also of the interior. Therefore, it is necessary first to characterize each target object sufficiently by a precursor mission to design the mission which then interacts with the object. In small solar system body (SSSB) science missions, this trend towards landing and sample-return missions is most apparent. It also has led to much interest in MASCOT-like landing modules and instrument carriers. They integrate at the instrument level to their mothership and by their size are compatible even with small interplanetary missions. The DLR-ESTEC GOSSAMER Roadmap NEA Science Working Groups‘ studies identified Multiple NEA Rendezvous (MNR) as one of the space science missions only feasible with solar sail propulsion. The parallel Solar Polar Orbiter (SPO) study showed the ability to access any inclination and a wide range of heliocentric distances. It used a separable payload module conducting the SPO mission after delivery by sail to the proper orbit. The Displaced L1 (DL1), spaceweather early warning mission study, outlined a very lightweight sailcraft operating close to Earth, where all objects of interest to planetary defence must pass. These and many other studies outline the unique capability of solar sails to provide access to all SSSB, at least within the orbit of Jupiter. Since the original MNR study, significant progress has been made to explore the performance envelope of near-term solar sails for multiple NEA rendezvous. However, although it is comparatively easy for solar sails to reach and rendezvous with objects in any inclination and in the complete range of semi-major axis and eccentricity relevant to NEOs and PHOs, it remains notoriously difficult for sailcraft to interact physically with a SSSB target object as e.g. the HAYABUSA missions do. The German Aerospace Center, DLR, recently brought the GOSSAMER solar sail deployment technology to qualification status in the GOSSAMER-1 project and continues the development of closely related technologies for very large deployable membrane-based photovoltaic arrays in the GOSOLAR project, on which we report separately. We expand the philosophy of the GOSSAMER solar sail concept of efficient multiple sub-spacecraft integration to also include landers for one-way in-situ investigations and sample-return missions. These are equally useful for planetary defence scenarios, SSSB science and NEO utilization. We outline the technological concept used to complete such missions and the synergetic integration and operation of sail and lander. We similarly extend the philosophy of MASCOT and use its characteristic features as well as the concept of Constraints-Driven Engineering for a wider range of operations. For example, the MASCOT Mobility hopping mechanism has already been adapted to the specific needs of MASCOT2. Utilizing sensors as well as predictions, those actuators could in a further development be used to implement anti-bouncing control schemes, by counteracting with the lander‘s rotation. Furthermore by introducing sudden jerk into the lander by utilization of the mobility, layers of loose regolith can be swirled up for sampling

Stress relaxation behaviour in IN718 nickel based superalloy during ageing heat treatments

Designing microstructure of components made from Inconel 718 nickel based superalloy (IN718) with tailored mechanical properties for high temperature applications, require sequential thermo-mechanical processing. This often includes straining and annealing at solution annealing temperature (i.e. ≈980℃) followed by water quenching and subsequent aging heat treatments at lower temperatures. In addition to the microstructure development (i.e. precipitation) the aging heat treatment partially relieve the residual stresses generated at previous stages of forging and water quenching, however the stress field will not be completely relaxed. In this study, a series of experiments were conducted on round tensile specimens made from IN718 bar to investigate tensile stress relaxation behaviours at elevated temperatures used for aging heat treatments. The stress relaxation curves obtained can be described by a hyperbolic function with a non-zero asymptotic stress (σ∞), which seems to be proportional to the initially applied stress (σ0) for a fixed temperature. This behaviour is investigated at temperatures between 620℃ and 770℃ that is a temperature range used in industry to perform the aging heat treatments to obtain microstructures with tailored mechanical properties. It has been shown that the σ∞/ σ0 ratio has decreased rapidly with increasing temperature at this range. The relaxation behaviour has been assessed numerically and an empirical relationship has been defined for each temperature that can be used for modelling purposes

Tidal influence on particulate organic carbon export fluxes

his study was supported through grant NE/G006415/1 of the UK’s Natural Environment Research Council (NERC) and grant 669947 of the European Research Council (ERC).As tall seamounts may be ‘stepping stones’ for dispersion and migration of deep open ocean fauna, an improved understanding of the productivity at and food supply to such systems needs to be formed. Here, the 234Th/238U approach for tracing settling particulate matter was applied to Senghor Seamount – a tall sub-marine mountain near the tropical Cape Verde archipelago – in order to elucidate the effects of topographically-influenced physical flow regimes on the export flux of particulate organic carbon (POC) from the near-surface (topmost ⩽ 100 m) into deeper waters. The comparison of a suitable reference site and the seamount sites revealed that POC export at the seamount sites was ∼2–4 times higher than at the reference site. For three out of five seamount sites, the calculated POC export fluxes are likely to be underestimates. If this is taken into account, it can be concluded that POC export fluxes increase while the passing waters are advected around and over the seamount, with the highest export fluxes occurring on the downstream side of the seamount. This supports the view that biogeochemical and biological effects of tall seamounts in surface-ocean waters might be strongest at some downstream distance from, rather than centred around, the seamount summit. Based on measured (vessel-mounted ADCP) and modelled (regional flow field: AVISO; internal tides at Senghor: MITgcm) flow dynamics, it is proposed that tidally generated internal waves result in a ‘screen’ of increased rates of energy dissipation that runs across the seamount and leads to a combination of two factors that caused the increased POC export above the seamount: (1) sudden increased upward transport of nutrients into the euphotic zone, driving brief pulses of primary production of new particulate matter, followed by the particles’ export into deeper waters; and (2) pulses of increased shear-driven aggregation of smaller, slower-settling into larger, faster-settling particles. This study shows that, under certain conditions, there can be an effect of a tall seamount on aspects of surface-ocean biogeochemistry, with tidal dynamics playing a prominent role. It is speculated that these effects can control the spatiotemporal distribution of magnitude and nutritional quality of the flux of food particles to the benthic and benthic-pelagic communities at and near tall seamounts.Publisher PDFPeer reviewe

Differential between Protein and mRNA Expression of CCR7 and SSTR5 Receptors in Crohn's Disease Patients

Crohn's disease (CD) is a multifactorial chronic inflammatory bowel disease of unknown cause. The aim of the present study was to explore if mRNA over-expression of SSTR5 and CCR7 found in CD patients could be correlated to respective protein expression. When compared to healthy donors, SSTR5 was over-expressed 417 ± 71 times in CD peripheral blood mononuclear cells (PBMCs). Flow cytometry experiments showed no correlation between mRNA and protein expression for SSTR5 in PBMCs. In an attempt to find a reason of such a high mRNA expression, SSTR5 present on CD PBMCs were tested and found as biologically active as on healthy cells. In biopsies of CD intestinal tissue, SSTR5 was not over-expressed but CCR7, unchanged in PBMCs, was over-expressed by 10 ± 3 times in the lamina propria. Confocal microscopy showed a good correlation of CCR7 mRNA and protein expression in CD intestinal biopsies. Our data emphasize flow and image cytometry as impossible to circumvent in complement to molecular biology so to avoid false interpretation on receptor expressions. Once confirmed by further large-scale studies, our preliminary results suggest a role for SSTR5 and CCR7 in CD pathogenesis