Magnetic and petrologic characterization of synthetic Martian basalts and implications for the surface magnetization of Mars

A suite of synthetic Martian basalts is generated with the objective of providing fundamental material properties data for use in modeling and interpretation of mission data. We systematically evaluate the effects of major element composition, oxygen fugacity (ƒO2), and cooling rate on phase chemistry and magnetic mineralogy, grain size, and intensity of remanent magnetization. The range of experimental compositions and ƒO2 are chosen to bracket the range expected in the Martian crust; our results should therefore span the range of possible mineralogies, textures, and magnetic properties in rapidly cooled Mars crustal materials. Two starting compositions are used for the sample synthesis: (1) an Fe-rich, Al-poor composition patterned after SNC basaltic meteorites and (2) a composition based on thermal emission spectrometer (TES) data with a much lower Fe/Al ratio. The resulting magnetic phase in samples generated at the quartz-fayalitemagnetite (QFM) buffer is a spinel-structured oxide with varying amounts of Cr, Ti, Mg, and Al. Compositional differences depend on bulk composition, cooling rate, differences in crystallization sequence, and the kinetics of silicate mineral nucleation and growth. Oxide abundance and magnetic intensity are most strongly influenced by fO2, with more subtle composition and cooling rate effects. Moderately oxidizing QFM conditions result in an intense magnetization (2.3 × 10-5 Am2 kg-1 to 1.4 × 10-2 Am2 kg-1), especially in the meteorite-derived basalts. However, an increase of magnetic grain size into the multidomain range (meteorite-type) and/or low unblocking temperatures resulting from increased Cr substitution (TES-type) may affect the long-term stability of the remanence in QFM samples

Advanced composite materials for precision segmented reflectors

The objective in the NASA Precision Segmented Reflector (PSR) project is to develop new composite material concepts for highly stable and durable reflectors with precision surfaces. The project focuses on alternate material concepts such as the development of new low coefficient of thermal expansion resins as matrices for graphite fiber reinforced composites, quartz fiber reinforced epoxies, and graphite reinforced glass. Low residual stress fabrication methods will be developed. When coupon specimens of these new material concepts have demonstrated the required surface accuracies and resistance to thermal distortion and microcracking, reflector panels will be fabricated and tested in simulated space environments. An important part of the program is the analytical modeling of environmental stability of these new composite materials concepts through constitutive equation development, modeling of microdamage in the composite matrix, and prediction of long term stability (including viscoelasticity). These analyses include both closed form and finite element solutions at the micro and macro levels

Multicomponent cubic oxide exsolution in synthetic basalts: Temperature dependence and implications for magnetic properties

Although the compositional unmixing of cubic-structured iron oxides has profound effects on the magnetic properties of rocks that contain them, a basic understanding of the kinetics and thermodynamics of this process has not been achieved in experimental studies due to sluggish reaction rates in binary oxide phases. Exploiting the fact that many natural Fe-oxides contain multiple additional cations, including Ti, Mg and Al, we perform novel “forward” laboratory experiments in which cubic-cubic phase exsolution proceeds from initially homogeneous multicomponent oxides. A variety of Fe-Ti-Mg-Al cubic iron oxides were nucleated and grown in synthetic, multicomponent basalt under different ƒO2 environments, and annealed at temperatures ranging from 590–790°C for up to 88 days. Fine-scale lamellar intergrowths of Fe-Ti-Al-Mg oxides, interpreted to represent cubic phase exsolution, were observed in seven samples, one that was synthesized and annealed at approximately constant ƒO2 (the quartz-fayalite-magnetite, or QFM, buffer) and six that were synthesized at very oxidizing conditions (~QFM + 6 log units) and then annealed at moderately oxidizing (~QFM) conditions. Results demonstrate that the consolute temperature of the multicomponent system is significantly higher than anneal temperatures and Curie temperatures, suggesting that samples that undergo this type of exsolution can carry a total thermal remanent magnetization. Exsolved samples are characterized by a dramatic increase in magnetization and coercivity, and a shift in Curie temperature(s), confirming predictions that this type of exsolution exerts strong control on the strength and stability of magnetization

Dialogue games for explaining medication choices

SMT solvers can be used efficiently to search for optimal paths across multiple graphs when optimising for certain resources. In the medical context, these graphs can represent treatment plans for chronic conditions where the optimal paths across all plans under consideration are the ones which minimize adverse drug interactions. The SMT solvers, however, work as a black-box model and there is a need to justify the optimal plans in a human-friendly way. We aim to fulfill this need by proposing explanatory dialogue protocols based on computational argumentation to increase the understanding and trust of humans interacting with the system. The protocols provide supporting reasons for nodes in a path and also allow counter reasons for the nodes not in the graph, highlighting any potential adverse interactions during the dialogue.Postprin

Asymptotically optimal quantum channel reversal for qudit ensembles and multimode Gaussian states

We investigate the problem of optimally reversing the action of an arbitrary quantum channel C which acts independently on each component of an ensemble of n identically prepared d-dimensional quantum systems. In the limit of large ensembles, we construct the optimal reversing channel R* which has to be applied at the output ensemble state, to retrieve a smaller ensemble of m systems prepared in the input state, with the highest possible rate m/n. The solution is found by mapping the problem into the optimal reversal of Gaussian channels on quantum-classical continuous variable systems, which is here solved as well. Our general results can be readily applied to improve the implementation of robust long-distance quantum communication. As an example, we investigate the optimal reversal rate of phase flip channels acting on a multi-qubit register.Comment: 17 pages, 3 figure

Evolutionary Roots of Property Rights; The Natural and Cultural Nature of Human Cooperation

Debates about the role of natural and cultural selection in the development of prosocial, antisocial and socially neutral mechanisms and behavior raise questions that touch property rights, cooperation, and conflict. For example, some researchers suggest that cooperation and prosociality evolved by natural selection (Hamilton 1964, Trivers 1971, Axelrod and Hamilton 1981, De Waal 2013, 2014), while others claim that natural selection is insufficient for the evolution of cooperation, which required in addition cultural selection (Sterelny 2013, Bowles and Gintis 2003, Seabright 2013, Norenzayan 2013). Some scholars focus on the complexity and hierarchical nature of the evolution of cooperation as involving different tools associated with lower and the higher levels of competition (Nowak 2006, Okasha 2006); others suggest that humans genetically inherited heuristics that favor prosocial behavior such as generosity, forgiveness or altruistic punishment (Ridley 1996, Bowles and Gintis 2004, Rolls 2005). We argue these mechanisms are not genetically inherited; rather, they are features inherited through cultural selection. To support this view we invoke inclusive fitness theory, which states that individuals tend to maximize their inclusive fitness, rather than maximizing group fitness. We further reject the older notion of natural group selection - as well as more recent versions (West, Mouden, Gardner 2011) – which hold that natural selection favors cooperators within a group (Wynne-Edwards 1962). For Wynne-Edwards, group selection leads to group adaptations; the survival of individuals therefore depends on the survival of the group and a sharing of resources. Individuals who do not cooperate, who are selfish, face extinction due to rapid and over-exploitation of resources

The Cosmic Ray Muon Flux at WIPP

In this work a measurement of the muon intensity at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, NM, USA is presented. WIPP is a salt mine with a depth of 655 m. The vertical muon flux was measured with a two panels scintillator coincidence setup to Phi_{vert}=3.10(+0.05/-0.07)*10^(-7)s^(-1)cm^(-2)sr^(-1).Comment: 18 pages, p figure