Kinetics of natural aging in Al-Mg-Si alloys studied by positron annihilation lifetime spectroscopy

The process of natural aging in pure ternary Al-Mg-Si alloys was studied by positron annihilation lifetime spectroscopy in real time in order to clarify the sequence and kinetics of clustering and precipitation. It was found that natural aging takes place in at least five stages in these alloys, four of which were directly observed. This is interpreted as the result of complex interactions between vacancies and solute atoms or clusters. One of the early stages of positron lifetime evolution coincides with a clustering process observed by differential scanning calorimetry (DSC) and involves the formation of a positron trap with \sim 0.200 ns lifetime. In later stages, a positron trap with a higher lifetime develops in coincidence with the DSC signal of a second clustering reaction. Mg governs both the kinetics and the lifetime change in this stage. Within the first 10 min after quenching, a period of nearly constant positron lifetime was found for those Mg-rich alloys that later show an insufficient hardness response to artificial aging, the so-called "negative effect." The various processes observed could be described by two effective activation energies that were found by varying the aging temperature from 10 to 37\degree C.Comment: arXiv admin note: same as v2, to correct mistaken v

Semiquantitative Infrared Analysis of Diketones and Anhydrides in a Reaction Mixture

The ozonolysis of a hydroxymethylene ketone yields a mixture of diketone and anhydride. Treatment of hydroxymethylene camphor with ozone affords, in addition to the expected camphor quinone, a surprisingly large amount of camphoric anhydride (56%) via Baeyer-Villager reaction. Use of infrared absorption to analyze the relative amounts of camphor quinone and camphoric anhydride in a reaction mixture was studied by comparing peak heights of their carbonyl stretching bands

The law relating to activities of man in space, chapters 5-7 Final report

Legal aspects of satellite communications, liability and space activities, natural resources, and pollution aspects of space exploratio

The law relating to activities of man in space, appendices A-D Final report

Jurisdiction over acts in outer space, domestic use of communication satellites, UN and other international agencies in controlling space, and bibliography on space law

The TWINS-LAD mission: Observations of terrestrial Lyman-? fluxes

International audienceThe TWINS project (Two Wide-angle Imaging Neutral-atom Spectrometers) is mainly devoted to measure high energy neutral atoms (ENAs) originating via charge exchange of protons with geocoronal hydrogen atoms in the plasmasphere and magnetosphere. In order to unfold the local ion density along the line-of-sight (LOS) from the integrated ENA flux measurements, a good knowledge of the geocoronal hydrogen density distribution is needed. Therefore, two Lyman-? detectors (LADs) - designed and calibrated by the authors - were added to the TWINS package. These detectors register line-integrated Lyman-? resonance emission intensities which then can be used to get the actual local hydrogen densities with the help of a numerical inversion routine

The 25 October 2010 Mentawai tsunami earthquake (M_w 7.8) and the tsunami hazard presented by shallow megathrust ruptures

The 25 October 2010 Mentawai, Indonesia earthquake (M_w 7.8) ruptured the shallow portion of the subduction zone seaward of the Mentawai islands, off-shore of Sumatra, generating 3 to 9 m tsunami run-up along southwestern coasts of the Pagai Islands that took at least 431 lives. Analyses of teleseismic P, SH and Rayleigh waves for finite-fault source rupture characteristics indicate ∼90 s rupture duration with a low rupture velocity of ∼1.5 km/s on the 10° dipping megathrust, with total slip of 2–4 m over an ∼100 km long source region. The seismic moment-scaled energy release is 1.4 × 10^(−6), lower than 2.4 × 10^(−6) found for the 17 July 2006 Java tsunami earthquake (M_w 7.8). The Mentawai event ruptured up-dip of the slip region of the 12 September 2007 Kepulauan earthquake (M_w 7.9), and together with the 4 January 1907 (M 7.6) tsunami earthquake located seaward of Simeulue Island to the northwest along the arc, demonstrates the significant tsunami generation potential for shallow megathrust ruptures in regions up-dip of great underthrusting events in Indonesia and elsewhere

Highly Efficient Midinfrared On-Chip Electrical Generation of Graphene Plasmons by Inelastic Electron Tunneling Excitation

Inelastic electron tunneling provides a low-energy pathway for the excitation of surface plasmons and light emission. We theoretically investigate tunnel junctions based on metals and graphene. We show that graphene is potentially a highly efficient material for tunneling excitation of plasmons because of its narrow plasmon linewidths, strong emission, and large tunability in the midinfrared wavelength regime. Compared to gold and silver, the enhancement can be up to 10 times for similar wavelengths and up to 5 orders at their respective plasmon operating wavelengths. Tunneling excitation of graphene plasmons promises an efficient technology for on-chip electrical generation and manipulation of plasmons for graphene-based optoelectronics and nanophotonic integrated circuits.Comment: 12 pages, 7 figure

A consistent thermodynamics of the MHD wave-heated two-fluid solar wind

International audienceWe start our considerations from two more recent findings in heliospheric physics: One is the fact that the primary solar wind protons do not cool off adiabatically with distance, but appear to be heated. The other one is that secondary protons, embedded in the solar wind as pick-up ions, behave quasi-isothermal at their motion to the outer heliosphere. These two phenomena must be physically closely connected with each other. To demonstrate this we solve a coupled set of enthalpy flow conservation equations for the two-fluid solar wind system consisting of primary and secondary protons. The coupling of these equations comes by the heat sources that are relevant, namely the dissipation of MHD turbulence power to the respective protons at the relevant dissipation scales. Hereby we consider both the dissipation of convected turbulences and the dissipation of turbulences locally driven by the injection of new pick-up ions into an unstable mode of the ion distribution function. Conversion of free kinetic energy of freshly injected secondary ions into turbulence power is finally followed by partial reabsorption of this energy both by primary and secondary ions. We show solutions of simultaneous integrations of the coupled set of differential thermodynamic two-fluid equations and can draw interesting conclusions from the solutions obtained. We can show that the secondary proton temperature with increasing radial distance asymptotically attains a constant value with a magnitude essentially determined by the actual solar wind velocity. Furthermore, we study the primary proton temperature within this two-fluid context and find a polytropic behaviour with radially and latitudinally variable polytropic indices determined by the local heat sources due to dissipated turbulent wave energy. Considering latitudinally variable solar wind conditions, as published by McComas et al. (2000), we also predict latitudinal variations of primary proton temperatures at large solar distances